diff options
| -rw-r--r-- | lib/Target/X86/X86TargetTransformInfo.cpp | 14 | ||||
| -rw-r--r-- | test/CodeGen/X86/constant-hoisting-cmp.ll | 25 |
2 files changed, 38 insertions, 1 deletions
diff --git a/lib/Target/X86/X86TargetTransformInfo.cpp b/lib/Target/X86/X86TargetTransformInfo.cpp index d33d5758412..09524251588 100644 --- a/lib/Target/X86/X86TargetTransformInfo.cpp +++ b/lib/Target/X86/X86TargetTransformInfo.cpp @@ -1199,6 +1199,19 @@ int X86TTIImpl::getIntImmCost(unsigned Opcode, unsigned Idx, const APInt &Imm, case Instruction::Store: ImmIdx = 0; break; + case Instruction::ICmp: + // This is an imperfect hack to prevent constant hoisting of + // compares that might be trying to check if a 64-bit value fits in + // 32-bits. The backend can optimize these cases using a right shift by 32. + // Ideally we would check the compare predicate here. There also other + // similar immediates the backend can use shifts for. + if (Idx == 1 && Imm.getBitWidth() == 64) { + uint64_t ImmVal = Imm.getZExtValue(); + if (ImmVal == 0x100000000ULL || ImmVal == 0xffffffff) + return TTI::TCC_Free; + } + ImmIdx = 1; + break; case Instruction::And: // We support 64-bit ANDs with immediates with 32-bits of leading zeroes // by using a 32-bit operation with implicit zero extension. Detect such @@ -1215,7 +1228,6 @@ int X86TTIImpl::getIntImmCost(unsigned Opcode, unsigned Idx, const APInt &Imm, case Instruction::SRem: case Instruction::Or: case Instruction::Xor: - case Instruction::ICmp: ImmIdx = 1; break; // Always return TCC_Free for the shift value of a shift instruction. diff --git a/test/CodeGen/X86/constant-hoisting-cmp.ll b/test/CodeGen/X86/constant-hoisting-cmp.ll new file mode 100644 index 00000000000..4e9e4948728 --- /dev/null +++ b/test/CodeGen/X86/constant-hoisting-cmp.ll @@ -0,0 +1,25 @@ +; RUN: llc < %s -O3 -march=x86-64 |FileCheck %s +define i64 @foo(i64 %data1, i64 %data2, i64 %data3) +{ +; If constant 4294967295 is hoisted to a variable, then we won't be able to +; use a shift right by 32 to optimize the compare. +entry: + %val1 = add i64 %data3, 1 + %x = icmp ugt i64 %data1, 4294967295 + br i1 %x, label %End, label %L_val2 + +; CHECK: shrq $32, {{.*}} +; CHECK: shrq $32, {{.*}} +L_val2: + %val2 = add i64 %data3, 2 + %y = icmp ugt i64 %data2, 4294967295 + br i1 %y, label %End, label %L_val3 + +L_val3: + %val3 = add i64 %data3, 3 + br label %End + +End: + %p1 = phi i64 [%val1,%entry], [%val2,%L_val2], [%val3,%L_val3] + ret i64 %p1 +} |