a105877646
The idea behind this canonicalization is that it allows us to handle less patterns, because we know that some will be canonicalized away. This is indeed very useful to e.g. know that constants are always on the right. However, this is only useful if the canonicalization is actually reliable. This is the case for constants, but not for arguments: Moving these to the right makes it look like the "more complex" expression is guaranteed to be on the left, but this is not actually the case in practice. It fails as soon as you replace the argument with another instruction. The end result is that it looks like things correctly work in tests, while they actually don't. We use the "thwart complexity-based canonicalization" trick to handle this in tests, but it's often a challenge for new contributors to get this right, and based on the regressions this PR originally exposed, we clearly don't get this right in many cases. For this reason, I think that it's better to remove this complexity canonicalization. It will make it much easier to write tests for commuted cases and make sure that they are handled.
59 lines
2.0 KiB
LLVM
59 lines
2.0 KiB
LLVM
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
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; RUN: opt < %s -passes=instcombine -S | FileCheck %s
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declare void @use.i8(i8)
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define i8 @fold_add_zext_eq_0(i8 %x) {
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; CHECK-LABEL: @fold_add_zext_eq_0(
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; CHECK-NEXT: [[R:%.*]] = call i8 @llvm.umax.i8(i8 [[X:%.*]], i8 1)
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; CHECK-NEXT: ret i8 [[R]]
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;
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%x_eq = icmp eq i8 %x, 0
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%x_eq_ext = zext i1 %x_eq to i8
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%r = add i8 %x, %x_eq_ext
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ret i8 %r
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}
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define <2 x i8> @fold_add_sext_eq_4_6(<2 x i6> %xx) {
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; CHECK-LABEL: @fold_add_sext_eq_4_6(
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; CHECK-NEXT: [[X:%.*]] = zext <2 x i6> [[XX:%.*]] to <2 x i8>
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; CHECK-NEXT: [[X_EQ:%.*]] = icmp eq <2 x i8> [[X]], <i8 4, i8 -127>
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; CHECK-NEXT: [[R:%.*]] = select <2 x i1> [[X_EQ]], <2 x i8> <i8 3, i8 -128>, <2 x i8> [[X]]
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; CHECK-NEXT: ret <2 x i8> [[R]]
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;
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%x = zext <2 x i6> %xx to <2 x i8>
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%x_eq = icmp eq <2 x i8> %x, <i8 4, i8 129>
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%x_eq_ext = sext <2 x i1> %x_eq to <2 x i8>
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%r = add <2 x i8> %x_eq_ext, %x
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ret <2 x i8> %r
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}
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define i8 @fold_add_zext_eq_0_fail_multiuse_exp(i8 %x) {
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; CHECK-LABEL: @fold_add_zext_eq_0_fail_multiuse_exp(
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; CHECK-NEXT: [[X_EQ:%.*]] = icmp eq i8 [[X:%.*]], 0
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; CHECK-NEXT: [[X_EQ_EXT:%.*]] = zext i1 [[X_EQ]] to i8
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; CHECK-NEXT: [[R:%.*]] = add i8 [[X]], [[X_EQ_EXT]]
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; CHECK-NEXT: call void @use.i8(i8 [[X_EQ_EXT]])
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; CHECK-NEXT: ret i8 [[R]]
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;
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%x_eq = icmp eq i8 %x, 0
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%x_eq_ext = zext i1 %x_eq to i8
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%r = add i8 %x, %x_eq_ext
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call void @use.i8(i8 %x_eq_ext)
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ret i8 %r
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}
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define i8 @fold_add_sext_eq_4_fail_wrong_cond(i8 %x, i8 %y) {
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; CHECK-LABEL: @fold_add_sext_eq_4_fail_wrong_cond(
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; CHECK-NEXT: [[X_EQ:%.*]] = icmp eq i8 [[Y:%.*]], 4
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; CHECK-NEXT: [[X_EQ_EXT:%.*]] = sext i1 [[X_EQ]] to i8
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; CHECK-NEXT: [[R:%.*]] = add i8 [[X:%.*]], [[X_EQ_EXT]]
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; CHECK-NEXT: call void @use.i8(i8 [[X_EQ_EXT]])
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; CHECK-NEXT: ret i8 [[R]]
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;
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%x_eq = icmp eq i8 %y, 4
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%x_eq_ext = sext i1 %x_eq to i8
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%r = add i8 %x, %x_eq_ext
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call void @use.i8(i8 %x_eq_ext)
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ret i8 %r
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}
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