2e3cabe172
Fix bug constants and sub instructions When finding constants in a chain starting with the RHS operator of sub instructions, we were negating the constant before zero extending it, which is incorrect. Unfortunately, I was unable to find a simple way to implement this transformation correctly, so for now I just disabled this optimization for constants that feed into the RHS of a sub. Resolves #62379 Transformation from alive2.llvm.org: define i16 @src(i8 %a, i8 %b, i8 %c) { entry: %0 = sub nuw nsw i8 %c, %a %1 = sub nuw nsw i8 %b, %0 %2 = zext i8 %1 to i16 ret i16 %2 } Before/Bad: define i16 @tgt(i8 %a, i8 %b, i8 %c) { entry: %0 = zext i8 %a to i16 %1 = zext i8 %b to i16 %c_neg = sub i8 0, %c %c_zext = zext i8 %c_neg to i16 %2 = sub i16 0, %0 %3 = sub i16 %1, %2 %4 = add i16 %3, %c_zext ret i16 %4 } Correct: define i16 @tgt(i8 %a, i8 %b, i8 %c) { entry: %0 = zext i8 %a to i16 %1 = zext i8 %b to i16 %c_zext = zext i8 %c to i16 %c_neg = sub i16 0, %c_zext %2 = sub i16 0, %0 %3 = sub i16 %1, %2 %4 = add i16 %3, %c_neg ret i16 %4 } Reviewed By: nikic Differential Revision: https://reviews.llvm.org/D149507
29 lines
1.2 KiB
LLVM
29 lines
1.2 KiB
LLVM
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 2
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; RUN: opt -S '-passes=separate-const-offset-from-gep<lower-gep>' < %s | FileCheck %s
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; These tests check that this pass does not incorrectly handle negative offsets.
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@c = internal constant [4 x i32] [i32 0, i32 1, i32 2, i32 3]
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; FIXME: We could optimize this case, but we don't currently. This test just
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; checks that we don't miscompile it.
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define i32 @sub_positive(i32 %a, i32 %b, ptr %ptr) {
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; CHECK-LABEL: define i32 @sub_positive
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; CHECK-SAME: (i32 [[A:%.*]], i32 [[B:%.*]], ptr [[PTR:%.*]]) {
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; CHECK-NEXT: entry:
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; CHECK-NEXT: [[TMP0:%.*]] = sub nuw nsw i32 15, [[A]]
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; CHECK-NEXT: [[TMP1:%.*]] = sub nuw nsw i32 [[B]], [[TMP0]]
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; CHECK-NEXT: [[TMP2:%.*]] = zext i32 [[TMP1]] to i64
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; CHECK-NEXT: [[TMP3:%.*]] = getelementptr inbounds [4 x i32], ptr [[PTR]], i64 0, i64 [[TMP2]]
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; CHECK-NEXT: [[TMP4:%.*]] = load i32, ptr [[TMP3]], align 4
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; CHECK-NEXT: ret i32 [[TMP4]]
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;
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entry:
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%0 = sub nuw nsw i32 15, %a
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%1 = sub nuw nsw i32 %b, %0
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%2 = zext i32 %1 to i64
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%3 = getelementptr inbounds [4 x i32], ptr %ptr, i64 0, i64 %2
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%4 = load i32, ptr %3
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ret i32 %4
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}
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