[ConstantHoisting][X86] Change the cost model to never hoist constants for types...

Currently the X86 backend doesn't support types larger than i128 very well. For
example an i192 multiply will assert in codegen when the 2nd argument is a constant and the constant got hoisted.

This fix changes the cost model to never hoist constants for types larger than
i128. Once the codegen issues have been resolved, the cost model can be updated
to allow also larger types.

This is related to <rdar://problem/16954938>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209162 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/X86/X86TargetTransformInfo.cpp b/lib/Target/X86/X86TargetTransformInfo.cpp
index 101574c84c3923ad08897e7444f3b318401b149b..69f34a16b6f77723945f7b98ee21c6265b77fd8d 100644 (file)
--- a/lib/Target/X86/X86TargetTransformInfo.cpp
+++ b/lib/Target/X86/X86TargetTransformInfo.cpp
@@ -815,6 +815,13 @@ unsigned X86TTI::getIntImmCost(const APInt &Imm, Type *Ty) const {
   if (BitSize == 0)
     return ~0U;
 
+  // Never hoist constants larger than 128bit, because this might lead to
+  // incorrect code generation or assertions in codegen.
+  // Fixme: Create a cost model for types larger than i128 once the codegen
+  // issues have been fixed.
+  if (BitSize > 128)
+    return TCC_Free;
+
   if (Imm == 0)
     return TCC_Free;
 
@@ -830,8 +837,10 @@ unsigned X86TTI::getIntImmCost(unsigned Opcode, unsigned Idx, const APInt &Imm,
   assert(Ty->isIntegerTy());
 
   unsigned BitSize = Ty->getPrimitiveSizeInBits();
+  // There is no cost model for constants with a bit size of 0. Return TCC_Free
+  // here, so that constant hoisting will ignore this constant.
   if (BitSize == 0)
-    return ~0U;
+    return TCC_Free;
 
   unsigned ImmIdx = ~0U;
   switch (Opcode) {
@@ -892,8 +901,10 @@ unsigned X86TTI::getIntImmCost(Intrinsic::ID IID, unsigned Idx,
   assert(Ty->isIntegerTy());
 
   unsigned BitSize = Ty->getPrimitiveSizeInBits();
+  // There is no cost model for constants with a bit size of 0. Return TCC_Free
+  // here, so that constant hoisting will ignore this constant.
   if (BitSize == 0)
-    return ~0U;
+    return TCC_Free;
 
   switch (IID) {
   default: return TCC_Free;

diff --git a/test/Transforms/ConstantHoisting/X86/large-immediate.ll b/test/Transforms/ConstantHoisting/X86/large-immediate.ll
index bd7fa40e9c593f3e074021d4c97e060cc0a0f2a1..e0af9c9be572665a3e1bfd220a5b7393fb6fbacf 100644 (file)
--- a/test/Transforms/ConstantHoisting/X86/large-immediate.ll
+++ b/test/Transforms/ConstantHoisting/X86/large-immediate.ll
@@ -16,3 +16,12 @@ define i512 @test2(i512 %a) nounwind {
   %2 = ashr i512 %1, 504
   ret i512 %2
 }
+
+; Check that we don't hoist constants with a type larger than i128.
+define i196 @test3(i196 %a) nounwind {
+; CHECK-LABEL: test3
+; CHECK-NOT: %const = bitcast i196 2 to i196
+  %1 = mul i196 %a, 2
+  %2 = mul i196 %1, 2
+  ret i196 %2
+}