[SelectionDAG] Constant fold (sext_inreg undef, VT) to 0 instead of undef.

The result of sign_extend_inreg needs to have as many sign bits
as requested by the VT argument. The easiest way to guarantee this
is to fold it to 0.

SystemZ test was modified to avoid using undef.

Fixes https://github.com/llvm/llvm-project/issues/55178

Reviewed By: RKSimon

Differential Revision: https://reviews.llvm.org/D124696

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index b93c99d..cc8fc67 100644 (file)
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -6225,9 +6225,9 @@ SDValue SelectionDAG::getNode(unsigned Opcode, const SDLoc &DL, EVT VT,
       std::swap(N1, N2);
     } else {
       switch (Opcode) {
-      case ISD::SIGN_EXTEND_INREG:
       case ISD::SUB:
         return getUNDEF(VT);     // fold op(undef, arg2) -> undef
+      case ISD::SIGN_EXTEND_INREG:
       case ISD::UDIV:
       case ISD::SDIV:
       case ISD::UREM:

diff --git a/llvm/test/CodeGen/AArch64/pr55178.ll b/llvm/test/CodeGen/AArch64/pr55178.ll
index 18a8ee8..d814d8e 100644 (file)
--- a/llvm/test/CodeGen/AArch64/pr55178.ll
+++ b/llvm/test/CodeGen/AArch64/pr55178.ll
@@ -10,8 +10,9 @@ define i1 @test14(i8 %X) {
 ; CHECK-NEXT:    mov w8, #-113
 ; CHECK-NEXT:    // kill: def $w0 killed $w0 def $x0
 ; CHECK-NEXT:    lsl w8, w8, w0
-; CHECK-NEXT:    cmp w8, w8, sxtb
-; CHECK-NEXT:    cset w0, lt
+; CHECK-NEXT:    sxtb w8, w8
+; CHECK-NEXT:    cmp w8, #0
+; CHECK-NEXT:    cset w0, gt
 ; CHECK-NEXT:    ret
   %1 = shl i8 -113, %X
   %cmp = icmp slt i8 undef, %1

diff --git a/llvm/test/CodeGen/SystemZ/regcoal_remat_empty_subrange.ll b/llvm/test/CodeGen/SystemZ/regcoal_remat_empty_subrange.ll
index 51e5b6b..0b87227 100644 (file)
--- a/llvm/test/CodeGen/SystemZ/regcoal_remat_empty_subrange.ll
+++ b/llvm/test/CodeGen/SystemZ/regcoal_remat_empty_subrange.ll
@@ -11,18 +11,19 @@
 @g_151 = external dso_local global i32, align 4
 @g_222 = external dso_local unnamed_addr global [7 x [10 x i8]], align 2
 
-define void @main() {
+define void @main(i16 %in) {
 ; CHECK-LABEL: main:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    lhi %r0, 1
+; CHECK-NEXT:    lhr %r2, %r2
 ; CHECK-NEXT:    larl %r1, g_151
 ; CHECK-NEXT:    lghi %r3, 0
-; CHECK-NEXT:    chi %r0, 0
+; CHECK-NEXT:    chi %r2, 0
+; CHECK-NEXT:    lhi %r0, 1
 ; CHECK-NEXT:    locghile %r3, 1
 ; CHECK-NEXT:    o %r0, 0(%r1)
-; CHECK-NEXT:    dsgfr %r2, %r0
 ; CHECK-NEXT:    larl %r1, g_222
 ; CHECK-NEXT:    lghi %r5, 0
+; CHECK-NEXT:    dsgfr %r2, %r0
 ; CHECK-NEXT:    stgrl %r2, g_39
 ; CHECK-NEXT:    stc %r5, 19(%r1)
 ; CHECK-NEXT:    br %r14
@@ -32,7 +33,7 @@ define void @main() {
   %tmp5 = srem i64 0, %tmp4
   %tmp6 = trunc i64 %tmp5 to i8
   store i8 %tmp6, i8* getelementptr inbounds ([7 x [10 x i8]], [7 x [10 x i8]]* @g_222, i64 0, i64 1, i64 9), align 1
-  %tmp7 = icmp slt i16 undef, 1
+  %tmp7 = icmp slt i16 %in, 1
   %tmp8 = zext i1 %tmp7 to i64
   %tmp9 = srem i64 %tmp8, %tmp4
   store i64 %tmp9, i64* @g_39, align 8