[llvm] 27a4371 - [InstCombine] Handle scalable splats of constants in getMinimumFPType (#132960)

[via llvm-commits]

Author: Luke Lau
Date: 2025-03-27T13:24:00Z
New Revision: 27a437108be83b217d9b7b8360fc40d42ae4458b

URL: https://github.com/llvm/llvm-project/commit/27a437108be83b217d9b7b8360fc40d42ae4458b
DIFF: https://github.com/llvm/llvm-project/commit/27a437108be83b217d9b7b8360fc40d42ae4458b.diff

LOG: [InstCombine] Handle scalable splats of constants in getMinimumFPType (#132960)

We previously handled ConstantExpr scalable splats in
5d929794a87602cfd873381e11cc99149196bb49, but only fpexts.

ConstantExpr fpexts have since been removed, and simultaneously we
didn't handle splats of constants that weren't extended.

This updates it to remove the fpext check and instead see if we can
shrink the result of getSplatValue.

Note that the test case doesn't get completely folded away due to
#132922

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
    llvm/test/Transforms/InstCombine/fpextend.ll
    llvm/test/Transforms/InstCombine/scalable-const-fp-splat.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
index 4ec1af394464b..1a95636f37ed7 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -1684,12 +1684,12 @@ static Type *getMinimumFPType(Value *V, bool PreferBFloat) {
     if (Type *T = shrinkFPConstant(CFP, PreferBFloat))
       return T;
 
-  // We can only correctly find a minimum type for a scalable vector when it is
-  // a splat. For splats of constant values the fpext is wrapped up as a
-  // ConstantExpr.
-  if (auto *FPCExt = dyn_cast<ConstantExpr>(V))
-    if (FPCExt->getOpcode() == Instruction::FPExt)
-      return FPCExt->getOperand(0)->getType();
+  // Try to shrink scalable and fixed splat vectors.
+  if (auto *FPC = dyn_cast<Constant>(V))
+    if (isa<VectorType>(V->getType()))
+      if (auto *Splat = dyn_cast_or_null<ConstantFP>(FPC->getSplatValue()))
+        if (Type *T = shrinkFPConstant(Splat, PreferBFloat))
+          return T;
 
   // Try to shrink a vector of FP constants. This returns nullptr on scalable
   // vectors

diff  --git a/llvm/test/Transforms/InstCombine/fpextend.ll b/llvm/test/Transforms/InstCombine/fpextend.ll
index c9adbe10d8db4..9125339c00ecf 100644
--- a/llvm/test/Transforms/InstCombine/fpextend.ll
+++ b/llvm/test/Transforms/InstCombine/fpextend.ll
@@ -448,3 +448,14 @@ define bfloat @bf16_frem(bfloat %x) {
   %t3 = fptrunc float %t2 to bfloat
   ret bfloat %t3
 }
+
+define <4 x float> @v4f32_fadd(<4 x float> %a) {
+; CHECK-LABEL: @v4f32_fadd(
+; CHECK-NEXT:    [[TMP1:%.*]] = fadd <4 x float> [[A:%.*]], splat (float -1.000000e+00)
+; CHECK-NEXT:    ret <4 x float> [[TMP1]]
+;
+  %2 = fpext <4 x float> %a to <4 x double>
+  %4 = fadd <4 x double> %2, splat (double -1.000000e+00)
+  %5 = fptrunc <4 x double> %4 to <4 x float>
+  ret <4 x float> %5
+}

diff  --git a/llvm/test/Transforms/InstCombine/scalable-const-fp-splat.ll b/llvm/test/Transforms/InstCombine/scalable-const-fp-splat.ll
index 731b079881f08..595486361d16e 100644
--- a/llvm/test/Transforms/InstCombine/scalable-const-fp-splat.ll
+++ b/llvm/test/Transforms/InstCombine/scalable-const-fp-splat.ll
@@ -13,3 +13,16 @@ define <vscale x 2 x float> @shrink_splat_scalable_extend(<vscale x 2 x float> %
   %5 = fptrunc <vscale x 2 x double> %4 to <vscale x 2 x float>
   ret <vscale x 2 x float> %5
 }
+
+define <vscale x 2 x float> @shrink_splat_scalable_extend_rhs_constexpr(<vscale x 2 x float> %a) {
+; CHECK-LABEL: define <vscale x 2 x float> @shrink_splat_scalable_extend_rhs_constexpr(
+; CHECK-SAME: <vscale x 2 x float> [[A:%.*]]) {
+; CHECK-NEXT:    [[TMP1:%.*]] = fptrunc <vscale x 2 x double> splat (double -1.000000e+00) to <vscale x 2 x float>
+; CHECK-NEXT:    [[TMP3:%.*]] = fadd <vscale x 2 x float> [[A]], [[TMP1]]
+; CHECK-NEXT:    ret <vscale x 2 x float> [[TMP3]]
+;
+  %2 = fpext <vscale x 2 x float> %a to <vscale x 2 x double>
+  %4 = fadd <vscale x 2 x double> %2, splat (double -1.000000e+00)
+  %5 = fptrunc <vscale x 2 x double> %4 to <vscale x 2 x float>
+  ret <vscale x 2 x float> %5
+}