[RISCV] Fix a bug in i32 FP_TO_UINT_SAT lowering on RV64.

We use the saturating behavior of fcvt.wu.h/s/d but forgot to
take into account that fcvt.wu will sign extend the saturated
result. According to computeKnownBits a promoted FP_TO_UINT_SAT
is expected to zero extend the saturated value.

In many case the upper bits aren't be demanded so this wouldn't
be an issue. But if we computeKnownBits caused an AND to be removed
it would be a bug.

This patch inserts an AND during to zero the upper bits.

Unfortunately, this pessimizes code if we aren't able to tell if
the upper bits are demanded. To fix that we could custom type
promote the FP_TO_UINT_SAT with SEXT_INREG after it, but I'll
leave that for future work.

I haven't found a failure from this, I was revisiting the code to
add vector support and spotted it.

Differential Revision: https://reviews.llvm.org/D133746

diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index e621c34..891af62 100644 (file)
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -1837,6 +1837,11 @@ static SDValue lowerFP_TO_INT_SAT(SDValue Op, SelectionDAG &DAG,
       Opc, DL, DstVT, Src,
       DAG.getTargetConstant(RISCVFPRndMode::RTZ, DL, Subtarget.getXLenVT()));
 
+  // fcvt.wu.* sign extends bit 31 on RV64. FP_TO_UINT_SAT expects to zero
+  // extend.
+  if (Opc == RISCVISD::FCVT_WU_RV64)
+    FpToInt = DAG.getZeroExtendInReg(FpToInt, DL, MVT::i32);
+
   SDValue ZeroInt = DAG.getConstant(0, DL, DstVT);
   return DAG.getSelectCC(DL, Src, Src, ZeroInt, FpToInt, ISD::CondCode::SETUO);
 }
@@ -8893,6 +8898,11 @@ static SDValue performFP_TO_INT_SATCombine(SDNode *N,
   SDValue FpToInt = DAG.getNode(Opc, DL, XLenVT, Src,
                                 DAG.getTargetConstant(FRM, DL, XLenVT));
 
+  // fcvt.wu.* sign extends bit 31 on RV64. FP_TO_UINT_SAT expects to zero
+  // extend.
+  if (Opc == RISCVISD::FCVT_WU_RV64)
+    FpToInt = DAG.getZeroExtendInReg(FpToInt, DL, MVT::i32);
+
   // RISCV FP-to-int conversions saturate to the destination register size, but
   // don't produce 0 for nan.
   SDValue ZeroInt = DAG.getConstant(0, DL, DstVT);

diff --git a/llvm/test/CodeGen/RISCV/double-convert.ll b/llvm/test/CodeGen/RISCV/double-convert.ll
index fc3790d..d35b57b 100644 (file)
--- a/llvm/test/CodeGen/RISCV/double-convert.ll
+++ b/llvm/test/CodeGen/RISCV/double-convert.ll
@@ -289,14 +289,25 @@ define i32 @fcvt_wu_d_multiple_use(double %x, i32* %y) nounwind {
 }
 
 define i32 @fcvt_wu_d_sat(double %a) nounwind {
-; CHECKIFD-LABEL: fcvt_wu_d_sat:
-; CHECKIFD:       # %bb.0: # %start
-; CHECKIFD-NEXT:    feq.d a0, fa0, fa0
-; CHECKIFD-NEXT:    beqz a0, .LBB6_2
-; CHECKIFD-NEXT:  # %bb.1:
-; CHECKIFD-NEXT:    fcvt.wu.d a0, fa0, rtz
-; CHECKIFD-NEXT:  .LBB6_2: # %start
-; CHECKIFD-NEXT:    ret
+; RV32IFD-LABEL: fcvt_wu_d_sat:
+; RV32IFD:       # %bb.0: # %start
+; RV32IFD-NEXT:    feq.d a0, fa0, fa0
+; RV32IFD-NEXT:    beqz a0, .LBB6_2
+; RV32IFD-NEXT:  # %bb.1:
+; RV32IFD-NEXT:    fcvt.wu.d a0, fa0, rtz
+; RV32IFD-NEXT:  .LBB6_2: # %start
+; RV32IFD-NEXT:    ret
+;
+; RV64IFD-LABEL: fcvt_wu_d_sat:
+; RV64IFD:       # %bb.0: # %start
+; RV64IFD-NEXT:    feq.d a0, fa0, fa0
+; RV64IFD-NEXT:    beqz a0, .LBB6_2
+; RV64IFD-NEXT:  # %bb.1:
+; RV64IFD-NEXT:    fcvt.wu.d a0, fa0, rtz
+; RV64IFD-NEXT:    slli a0, a0, 32
+; RV64IFD-NEXT:    srli a0, a0, 32
+; RV64IFD-NEXT:  .LBB6_2: # %start
+; RV64IFD-NEXT:    ret
 ;
 ; RV32I-LABEL: fcvt_wu_d_sat:
 ; RV32I:       # %bb.0: # %start
@@ -1965,14 +1976,25 @@ start:
 declare i8 @llvm.fptoui.sat.i8.f64(double)
 
 define zeroext i32 @fcvt_wu_d_sat_zext(double %a) nounwind {
-; CHECKIFD-LABEL: fcvt_wu_d_sat_zext:
-; CHECKIFD:       # %bb.0: # %start
-; CHECKIFD-NEXT:    feq.d a0, fa0, fa0
-; CHECKIFD-NEXT:    beqz a0, .LBB33_2
-; CHECKIFD-NEXT:  # %bb.1:
-; CHECKIFD-NEXT:    fcvt.wu.d a0, fa0, rtz
-; CHECKIFD-NEXT:  .LBB33_2: # %start
-; CHECKIFD-NEXT:    ret
+; RV32IFD-LABEL: fcvt_wu_d_sat_zext:
+; RV32IFD:       # %bb.0: # %start
+; RV32IFD-NEXT:    feq.d a0, fa0, fa0
+; RV32IFD-NEXT:    beqz a0, .LBB33_2
+; RV32IFD-NEXT:  # %bb.1:
+; RV32IFD-NEXT:    fcvt.wu.d a0, fa0, rtz
+; RV32IFD-NEXT:  .LBB33_2: # %start
+; RV32IFD-NEXT:    ret
+;
+; RV64IFD-LABEL: fcvt_wu_d_sat_zext:
+; RV64IFD:       # %bb.0: # %start
+; RV64IFD-NEXT:    feq.d a0, fa0, fa0
+; RV64IFD-NEXT:    beqz a0, .LBB33_2
+; RV64IFD-NEXT:  # %bb.1:
+; RV64IFD-NEXT:    fcvt.wu.d a0, fa0, rtz
+; RV64IFD-NEXT:    slli a0, a0, 32
+; RV64IFD-NEXT:    srli a0, a0, 32
+; RV64IFD-NEXT:  .LBB33_2: # %start
+; RV64IFD-NEXT:    ret
 ;
 ; RV32I-LABEL: fcvt_wu_d_sat_zext:
 ; RV32I:       # %bb.0: # %start

diff --git a/llvm/test/CodeGen/RISCV/float-convert.ll b/llvm/test/CodeGen/RISCV/float-convert.ll
index 7737e86..5b62d46 100644 (file)
--- a/llvm/test/CodeGen/RISCV/float-convert.ll
+++ b/llvm/test/CodeGen/RISCV/float-convert.ll
@@ -216,14 +216,25 @@ define i32 @fcvt_wu_s_multiple_use(float %x, i32* %y) nounwind {
 }
 
 define i32 @fcvt_wu_s_sat(float %a) nounwind {
-; CHECKIF-LABEL: fcvt_wu_s_sat:
-; CHECKIF:       # %bb.0: # %start
-; CHECKIF-NEXT:    feq.s a0, fa0, fa0
-; CHECKIF-NEXT:    beqz a0, .LBB4_2
-; CHECKIF-NEXT:  # %bb.1:
-; CHECKIF-NEXT:    fcvt.wu.s a0, fa0, rtz
-; CHECKIF-NEXT:  .LBB4_2: # %start
-; CHECKIF-NEXT:    ret
+; RV32IF-LABEL: fcvt_wu_s_sat:
+; RV32IF:       # %bb.0: # %start
+; RV32IF-NEXT:    feq.s a0, fa0, fa0
+; RV32IF-NEXT:    beqz a0, .LBB4_2
+; RV32IF-NEXT:  # %bb.1:
+; RV32IF-NEXT:    fcvt.wu.s a0, fa0, rtz
+; RV32IF-NEXT:  .LBB4_2: # %start
+; RV32IF-NEXT:    ret
+;
+; RV64IF-LABEL: fcvt_wu_s_sat:
+; RV64IF:       # %bb.0: # %start
+; RV64IF-NEXT:    feq.s a0, fa0, fa0
+; RV64IF-NEXT:    beqz a0, .LBB4_2
+; RV64IF-NEXT:  # %bb.1:
+; RV64IF-NEXT:    fcvt.wu.s a0, fa0, rtz
+; RV64IF-NEXT:    slli a0, a0, 32
+; RV64IF-NEXT:    srli a0, a0, 32
+; RV64IF-NEXT:  .LBB4_2: # %start
+; RV64IF-NEXT:    ret
 ;
 ; RV32I-LABEL: fcvt_wu_s_sat:
 ; RV32I:       # %bb.0: # %start
@@ -1768,14 +1779,25 @@ start:
 declare i8 @llvm.fptoui.sat.i8.f32(float)
 
 define zeroext i32 @fcvt_wu_s_sat_zext(float %a) nounwind {
-; CHECKIF-LABEL: fcvt_wu_s_sat_zext:
-; CHECKIF:       # %bb.0: # %start
-; CHECKIF-NEXT:    feq.s a0, fa0, fa0
-; CHECKIF-NEXT:    beqz a0, .LBB31_2
-; CHECKIF-NEXT:  # %bb.1:
-; CHECKIF-NEXT:    fcvt.wu.s a0, fa0, rtz
-; CHECKIF-NEXT:  .LBB31_2: # %start
-; CHECKIF-NEXT:    ret
+; RV32IF-LABEL: fcvt_wu_s_sat_zext:
+; RV32IF:       # %bb.0: # %start
+; RV32IF-NEXT:    feq.s a0, fa0, fa0
+; RV32IF-NEXT:    beqz a0, .LBB31_2
+; RV32IF-NEXT:  # %bb.1:
+; RV32IF-NEXT:    fcvt.wu.s a0, fa0, rtz
+; RV32IF-NEXT:  .LBB31_2: # %start
+; RV32IF-NEXT:    ret
+;
+; RV64IF-LABEL: fcvt_wu_s_sat_zext:
+; RV64IF:       # %bb.0: # %start
+; RV64IF-NEXT:    feq.s a0, fa0, fa0
+; RV64IF-NEXT:    beqz a0, .LBB31_2
+; RV64IF-NEXT:  # %bb.1:
+; RV64IF-NEXT:    fcvt.wu.s a0, fa0, rtz
+; RV64IF-NEXT:    slli a0, a0, 32
+; RV64IF-NEXT:    srli a0, a0, 32
+; RV64IF-NEXT:  .LBB31_2: # %start
+; RV64IF-NEXT:    ret
 ;
 ; RV32I-LABEL: fcvt_wu_s_sat_zext:
 ; RV32I:       # %bb.0: # %start

diff --git a/llvm/test/CodeGen/RISCV/half-convert.ll b/llvm/test/CodeGen/RISCV/half-convert.ll
index e5c6b3a..b582ac2 100644 (file)
--- a/llvm/test/CodeGen/RISCV/half-convert.ll
+++ b/llvm/test/CodeGen/RISCV/half-convert.ll
@@ -690,14 +690,25 @@ define i32 @fcvt_wu_h_multiple_use(half %x, i32* %y) nounwind {
 }
 
 define i32 @fcvt_wu_h_sat(half %a) nounwind {
-; CHECKIZFH-LABEL: fcvt_wu_h_sat:
-; CHECKIZFH:       # %bb.0: # %start
-; CHECKIZFH-NEXT:    feq.h a0, fa0, fa0
-; CHECKIZFH-NEXT:    beqz a0, .LBB8_2
-; CHECKIZFH-NEXT:  # %bb.1:
-; CHECKIZFH-NEXT:    fcvt.wu.h a0, fa0, rtz
-; CHECKIZFH-NEXT:  .LBB8_2: # %start
-; CHECKIZFH-NEXT:    ret
+; RV32IZFH-LABEL: fcvt_wu_h_sat:
+; RV32IZFH:       # %bb.0: # %start
+; RV32IZFH-NEXT:    feq.h a0, fa0, fa0
+; RV32IZFH-NEXT:    beqz a0, .LBB8_2
+; RV32IZFH-NEXT:  # %bb.1:
+; RV32IZFH-NEXT:    fcvt.wu.h a0, fa0, rtz
+; RV32IZFH-NEXT:  .LBB8_2: # %start
+; RV32IZFH-NEXT:    ret
+;
+; RV64IZFH-LABEL: fcvt_wu_h_sat:
+; RV64IZFH:       # %bb.0: # %start
+; RV64IZFH-NEXT:    feq.h a0, fa0, fa0
+; RV64IZFH-NEXT:    beqz a0, .LBB8_2
+; RV64IZFH-NEXT:  # %bb.1:
+; RV64IZFH-NEXT:    fcvt.wu.h a0, fa0, rtz
+; RV64IZFH-NEXT:    slli a0, a0, 32
+; RV64IZFH-NEXT:    srli a0, a0, 32
+; RV64IZFH-NEXT:  .LBB8_2: # %start
+; RV64IZFH-NEXT:    ret
 ;
 ; RV32IDZFH-LABEL: fcvt_wu_h_sat:
 ; RV32IDZFH:       # %bb.0: # %start
@@ -714,6 +725,8 @@ define i32 @fcvt_wu_h_sat(half %a) nounwind {
 ; RV64IDZFH-NEXT:    beqz a0, .LBB8_2
 ; RV64IDZFH-NEXT:  # %bb.1:
 ; RV64IDZFH-NEXT:    fcvt.wu.h a0, fa0, rtz
+; RV64IDZFH-NEXT:    slli a0, a0, 32
+; RV64IDZFH-NEXT:    srli a0, a0, 32
 ; RV64IDZFH-NEXT:  .LBB8_2: # %start
 ; RV64IDZFH-NEXT:    ret
 ;
@@ -3019,14 +3032,25 @@ start:
 declare i8 @llvm.fptoui.sat.i8.f16(half)
 
 define zeroext i32 @fcvt_wu_h_sat_zext(half %a) nounwind {
-; CHECKIZFH-LABEL: fcvt_wu_h_sat_zext:
-; CHECKIZFH:       # %bb.0: # %start
-; CHECKIZFH-NEXT:    feq.h a0, fa0, fa0
-; CHECKIZFH-NEXT:    beqz a0, .LBB39_2
-; CHECKIZFH-NEXT:  # %bb.1:
-; CHECKIZFH-NEXT:    fcvt.wu.h a0, fa0, rtz
-; CHECKIZFH-NEXT:  .LBB39_2: # %start
-; CHECKIZFH-NEXT:    ret
+; RV32IZFH-LABEL: fcvt_wu_h_sat_zext:
+; RV32IZFH:       # %bb.0: # %start
+; RV32IZFH-NEXT:    feq.h a0, fa0, fa0
+; RV32IZFH-NEXT:    beqz a0, .LBB39_2
+; RV32IZFH-NEXT:  # %bb.1:
+; RV32IZFH-NEXT:    fcvt.wu.h a0, fa0, rtz
+; RV32IZFH-NEXT:  .LBB39_2: # %start
+; RV32IZFH-NEXT:    ret
+;
+; RV64IZFH-LABEL: fcvt_wu_h_sat_zext:
+; RV64IZFH:       # %bb.0: # %start
+; RV64IZFH-NEXT:    feq.h a0, fa0, fa0
+; RV64IZFH-NEXT:    beqz a0, .LBB39_2
+; RV64IZFH-NEXT:  # %bb.1:
+; RV64IZFH-NEXT:    fcvt.wu.h a0, fa0, rtz
+; RV64IZFH-NEXT:    slli a0, a0, 32
+; RV64IZFH-NEXT:    srli a0, a0, 32
+; RV64IZFH-NEXT:  .LBB39_2: # %start
+; RV64IZFH-NEXT:    ret
 ;
 ; RV32IDZFH-LABEL: fcvt_wu_h_sat_zext:
 ; RV32IDZFH:       # %bb.0: # %start
@@ -3043,6 +3067,8 @@ define zeroext i32 @fcvt_wu_h_sat_zext(half %a) nounwind {
 ; RV64IDZFH-NEXT:    beqz a0, .LBB39_2
 ; RV64IDZFH-NEXT:  # %bb.1:
 ; RV64IDZFH-NEXT:    fcvt.wu.h a0, fa0, rtz
+; RV64IDZFH-NEXT:    slli a0, a0, 32
+; RV64IDZFH-NEXT:    srli a0, a0, 32
 ; RV64IDZFH-NEXT:  .LBB39_2: # %start
 ; RV64IDZFH-NEXT:    ret
 ;