[PATCH] D79116: [InstCombine] fold fpext into Xitofp

[Sanjay Patel via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rGa62533c29f84: [InstCombine] fold fpext into exact integer-to-FP cast (authored by spatel).

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D79116/new/

https://reviews.llvm.org/D79116

Files:
  llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
  llvm/test/Transforms/InstCombine/fpextend.ll


Index: llvm/test/Transforms/InstCombine/fpextend.ll
===================================================================
--- llvm/test/Transforms/InstCombine/fpextend.ll
+++ llvm/test/Transforms/InstCombine/fpextend.ll
@@ -259,10 +259,11 @@
   ret float %t56
 }
 
+; Convert from integer is exact, so convert directly to double.
+
 define double @ItoFtoF_s25_f32_f64(i25 %i) {
 ; CHECK-LABEL: @ItoFtoF_s25_f32_f64(
-; CHECK-NEXT:    [[X:%.*]] = sitofp i25 [[I:%.*]] to float
-; CHECK-NEXT:    [[R:%.*]] = fpext float [[X]] to double
+; CHECK-NEXT:    [[R:%.*]] = sitofp i25 [[I:%.*]] to double
 ; CHECK-NEXT:    ret double [[R]]
 ;
   %x = sitofp i25 %i to float
@@ -270,10 +271,11 @@
   ret double %r
 }
 
+; Convert from integer is exact, so convert directly to fp128.
+
 define fp128 @ItoFtoF_u24_f32_f128(i24 %i) {
 ; CHECK-LABEL: @ItoFtoF_u24_f32_f128(
-; CHECK-NEXT:    [[X:%.*]] = uitofp i24 [[I:%.*]] to float
-; CHECK-NEXT:    [[R:%.*]] = fpext float [[X]] to fp128
+; CHECK-NEXT:    [[R:%.*]] = uitofp i24 [[I:%.*]] to fp128
 ; CHECK-NEXT:    ret fp128 [[R]]
 ;
   %x = uitofp i24 %i to float
@@ -281,6 +283,8 @@
   ret fp128 %r
 }
 
+; Negative test - intermediate rounding in float type.
+
 define double @ItoFtoF_s26_f32_f64(i26 %i) {
 ; CHECK-LABEL: @ItoFtoF_s26_f32_f64(
 ; CHECK-NEXT:    [[X:%.*]] = sitofp i26 [[I:%.*]] to float
@@ -292,6 +296,8 @@
   ret double %r
 }
 
+; Negative test - intermediate rounding in float type.
+
 define double @ItoFtoF_u25_f32_f64(i25 %i) {
 ; CHECK-LABEL: @ItoFtoF_u25_f32_f64(
 ; CHECK-NEXT:    [[X:%.*]] = uitofp i25 [[I:%.*]] to float
Index: llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -1757,8 +1757,18 @@
   return false;
 }
 
-Instruction *InstCombiner::visitFPExt(CastInst &CI) {
-  return commonCastTransforms(CI);
+Instruction *InstCombiner::visitFPExt(CastInst &FPExt) {
+  // If the source operand is a cast from integer to FP and known exact, then
+  // cast the integer operand directly to the destination type.
+  Type *Ty = FPExt.getType();
+  Value *Src = FPExt.getOperand(0);
+  if (isa<SIToFPInst>(Src) || isa<UIToFPInst>(Src)) {
+    auto *FPCast = cast<CastInst>(Src);
+    if (isKnownExactCastIntToFP(*FPCast))
+      return CastInst::Create(FPCast->getOpcode(), FPCast->getOperand(0), Ty);
+  }
+
+  return commonCastTransforms(FPExt);
 }
 
 /// fpto{s/u}i({u/s}itofp(X)) --> X or zext(X) or sext(X) or trunc(X)


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