[PATCH] D43774: [InstCombine] Add constant vector support to getMinimumFPType for visitFPTrunc.

[Craig Topper via Phabricator via llvm-commits]

craig.topper updated this revision to Diff 136844.
craig.topper retitled this revision from "[InstCombine] Add constant vector support to lookThroughFPExtensions for visitFPTrunc." to "[InstCombine] Add constant vector support to getMinimumFPType for visitFPTrunc.".
craig.topper added a comment.

The scalar code is now type based and doesn't new constants. Rework this patch to build on that and find a minimal safe type by looking at each element. Then turn that into a vector type.


https://reviews.llvm.org/D43774

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


Index: test/Transforms/InstCombine/fpextend.ll
===================================================================
--- test/Transforms/InstCombine/fpextend.ll
+++ test/Transforms/InstCombine/fpextend.ll
@@ -59,9 +59,7 @@
 define <2 x float> @test5(<2 x float> %x) nounwind  {
 ; CHECK-LABEL: @test5(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[TMP1:%.*]] = fpext <2 x float> [[X:%.*]] to <2 x double>
-; CHECK-NEXT:    [[TMP3:%.*]] = fadd <2 x double> [[TMP1]], zeroinitializer
-; CHECK-NEXT:    [[TMP34:%.*]] = fptrunc <2 x double> [[TMP3]] to <2 x float>
+; CHECK-NEXT:    [[TMP34:%.*]] = fadd <2 x float> [[X:%.*]], zeroinitializer
 ; CHECK-NEXT:    ret <2 x float> [[TMP34]]
 ;
 entry:
@@ -75,9 +73,7 @@
 define <2 x float> @test6(<2 x float> %x) nounwind  {
 ; CHECK-LABEL: @test6(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[TMP1:%.*]] = fpext <2 x float> [[X:%.*]] to <2 x double>
-; CHECK-NEXT:    [[TMP3:%.*]] = fadd <2 x double> [[TMP1]], <double 0.000000e+00, double -0.000000e+00>
-; CHECK-NEXT:    [[TMP34:%.*]] = fptrunc <2 x double> [[TMP3]] to <2 x float>
+; CHECK-NEXT:    [[TMP34:%.*]] = fadd <2 x float> [[X:%.*]], <float 0.000000e+00, float -0.000000e+00>
 ; CHECK-NEXT:    ret <2 x float> [[TMP34]]
 ;
 entry:
@@ -89,9 +85,7 @@
 
 define <2 x float> @not_half_shrinkable(<2 x float> %x) {
 ; CHECK-LABEL: @not_half_shrinkable(
-; CHECK-NEXT:    [[EXT:%.*]] = fpext <2 x float> [[X:%.*]] to <2 x double>
-; CHECK-NEXT:    [[ADD:%.*]] = fadd <2 x double> [[EXT]], <double 0.000000e+00, double 2.049000e+03>
-; CHECK-NEXT:    [[R:%.*]] = fptrunc <2 x double> [[ADD]] to <2 x float>
+; CHECK-NEXT:    [[R:%.*]] = fadd <2 x float> [[X:%.*]], <float 0.000000e+00, float 2.049000e+03>
 ; CHECK-NEXT:    ret <2 x float> [[R]]
 ;
   %ext = fpext <2 x float> %x to <2 x double>
Index: lib/Transforms/InstCombine/InstCombineCasts.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -1435,6 +1435,35 @@
   return nullptr;
 }
 
+// Determine if this is a vector of ConstantFPs and if so, return the minimal
+// type we can safely truncate all elements to.
+static Type *shrinkFPConstantVector(Value *V) {
+  auto *CV = dyn_cast<Constant>(V);
+  if (!CV || !CV->getType()->isVectorTy())
+    return nullptr;
+
+  Type *MinType = nullptr;
+
+  unsigned NumElts = CV->getType()->getVectorNumElements();
+  for (unsigned i = 0; i != NumElts; ++i) {
+    auto *CFP = dyn_cast_or_null<ConstantFP>(CV->getAggregateElement(i));
+    if (!CFP)
+      return nullptr;
+
+    Type *T = shrinkFPConstant(CFP);
+    if (!T)
+      return nullptr;
+
+    // If we haven't found a type yet or this type has a larger mantissa than
+    // our previous type, this is our new minimal type.
+    if (!MinType || T->getFPMantissaWidth() > MinType->getFPMantissaWidth())
+      MinType = T;
+  }
+
+  // Make a vector type from the minimal type.
+  return VectorType::get(MinType, NumElts);
+}
+
 /// Find the minimum FP type we can safely truncate to.
 static Type *getMinimumFPType(Value *V) {
   if (auto *FPExt = dyn_cast<FPExtInst>(V))
@@ -1447,6 +1476,10 @@
     if (Type *T = shrinkFPConstant(CFP))
       return T;
 
+  // Try to shrink a vector of FP constants.
+  if (Type *T = shrinkFPConstantVector(V))
+    return T;
+
   return V->getType();
 }
 


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