[InstCombine] Only fold trunc(ext) pairs to bitcast if the source and destination...

This used to be always the case, but the addition of bfloat to the type
matrix makes this invalid.

diff --git a/llvm/lib/IR/Instructions.cpp b/llvm/lib/IR/Instructions.cpp
index 7615a4d..1b546ce 100644 (file)
--- a/llvm/lib/IR/Instructions.cpp
+++ b/llvm/lib/IR/Instructions.cpp
@@ -3088,16 +3088,18 @@ unsigned CastInst::isEliminableCastPair(
       return 0;
     }
     case 8: {
-      // ext, trunc -> bitcast,    if the SrcTy and DstTy are same size
+      // ext, trunc -> bitcast,    if the SrcTy and DstTy are the same
       // ext, trunc -> ext,        if sizeof(SrcTy) < sizeof(DstTy)
       // ext, trunc -> trunc,      if sizeof(SrcTy) > sizeof(DstTy)
       unsigned SrcSize = SrcTy->getScalarSizeInBits();
       unsigned DstSize = DstTy->getScalarSizeInBits();
-      if (SrcSize == DstSize)
+      if (SrcTy == DstTy)
         return Instruction::BitCast;
-      else if (SrcSize < DstSize)
+      if (SrcSize < DstSize)
         return firstOp;
-      return secondOp;
+      if (SrcSize > DstSize)
+        return secondOp;
+      return 0;
     }
     case 9:
       // zext, sext -> zext, because sext can't sign extend after zext

diff --git a/llvm/test/Transforms/InstCombine/fpextend.ll b/llvm/test/Transforms/InstCombine/fpextend.ll
index 13784c6..c991f5d 100644 (file)
--- a/llvm/test/Transforms/InstCombine/fpextend.ll
+++ b/llvm/test/Transforms/InstCombine/fpextend.ll
@@ -429,3 +429,14 @@ define double @FtoItoFtoF_f32_su32_f32_f64(float %f) {
   %r = fpext float %x to double
   ret double %r
 }
+
+define half @bf16_to_f32_to_f16(bfloat %a) nounwind {
+; CHECK-LABEL: @bf16_to_f32_to_f16(
+; CHECK-NEXT:    [[Y:%.*]] = fpext bfloat [[A:%.*]] to float
+; CHECK-NEXT:    [[Z:%.*]] = fptrunc float [[Y]] to half
+; CHECK-NEXT:    ret half [[Z]]
+;
+  %y = fpext bfloat %a to float
+  %z = fptrunc float %y to half
+  ret half %z
+}