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llvm-project/llvm/test/Transforms/InstCombine/pr44242.ll
Nikita Popov a105877646
[InstCombine] Remove some of the complexity-based canonicalization (#91185) 
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.
2024-08-21 12:02:54 +02:00

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; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt -S -passes=instcombine < %s | FileCheck %s
; Check that we don't create two redundant phi nodes when %val is used in a
; form where we can't rewrite it in terms of the new phi node.
; Use %val in an instruction type not supported by optimizeBitCastFromPhi.
define float @sitofp(float %x) {
; CHECK-LABEL: @sitofp(
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[LOOP_HEADER:%.*]]
; CHECK: loop_header:
; CHECK-NEXT: [[VAL:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[VAL_INCR_CASTED:%.*]], [[LOOP:%.*]] ]
; CHECK-NEXT: [[VAL_CASTED:%.*]] = bitcast i32 [[VAL]] to float
; CHECK-NEXT: [[CMP:%.*]] = fcmp olt float [[X:%.*]], [[VAL_CASTED]]
; CHECK-NEXT: br i1 [[CMP]], label [[END:%.*]], label [[LOOP]]
; CHECK: loop:
; CHECK-NEXT: [[VAL_INCR:%.*]] = fadd float [[VAL_CASTED]], 1.000000e+00
; CHECK-NEXT: [[VAL_INCR_CASTED]] = bitcast float [[VAL_INCR]] to i32
; CHECK-NEXT: br label [[LOOP_HEADER]]
; CHECK: end:
; CHECK-NEXT: [[RESULT:%.*]] = sitofp i32 [[VAL]] to float
; CHECK-NEXT: ret float [[RESULT]]
;
entry:
br label %loop_header
loop_header:
%val = phi i32 [ 0, %entry ], [ %val_incr_casted, %loop ]
%val_casted = bitcast i32 %val to float
%cmp = fcmp ogt float %val_casted, %x
br i1 %cmp, label %end, label %loop
loop:
%val_incr = fadd float %val_casted, 1.0
%val_incr_casted = bitcast float %val_incr to i32
br label %loop_header
end:
%result = sitofp i32 %val to float
ret float %result
}
; Use %val in an incompatible bitcast.
define <2 x i16> @bitcast(float %x) {
; CHECK-LABEL: @bitcast(
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[LOOP_HEADER:%.*]]
; CHECK: loop_header:
; CHECK-NEXT: [[VAL:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[VAL_INCR_CASTED:%.*]], [[LOOP:%.*]] ]
; CHECK-NEXT: [[VAL_CASTED:%.*]] = bitcast i32 [[VAL]] to float
; CHECK-NEXT: [[CMP:%.*]] = fcmp olt float [[X:%.*]], [[VAL_CASTED]]
; CHECK-NEXT: br i1 [[CMP]], label [[END:%.*]], label [[LOOP]]
; CHECK: loop:
; CHECK-NEXT: [[VAL_INCR:%.*]] = fadd float [[VAL_CASTED]], 1.000000e+00
; CHECK-NEXT: [[VAL_INCR_CASTED]] = bitcast float [[VAL_INCR]] to i32
; CHECK-NEXT: br label [[LOOP_HEADER]]
; CHECK: end:
; CHECK-NEXT: [[RESULT:%.*]] = bitcast i32 [[VAL]] to <2 x i16>
; CHECK-NEXT: ret <2 x i16> [[RESULT]]
;
entry:
br label %loop_header
loop_header:
%val = phi i32 [ 0, %entry ], [ %val_incr_casted, %loop ]
%val_casted = bitcast i32 %val to float
%cmp = fcmp ogt float %val_casted, %x
br i1 %cmp, label %end, label %loop
loop:
%val_incr = fadd float %val_casted, 1.0
%val_incr_casted = bitcast float %val_incr to i32
br label %loop_header
end:
%result = bitcast i32 %val to <2 x i16>
ret <2 x i16> %result
}
@global = global i32 0
; Use %val with a volatile store.
define void @store_volatile(float %x) {
; CHECK-LABEL: @store_volatile(
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[LOOP_HEADER:%.*]]
; CHECK: loop_header:
; CHECK-NEXT: [[VAL:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[VAL_INCR_CASTED:%.*]], [[LOOP:%.*]] ]
; CHECK-NEXT: [[VAL_CASTED:%.*]] = bitcast i32 [[VAL]] to float
; CHECK-NEXT: [[CMP:%.*]] = fcmp olt float [[X:%.*]], [[VAL_CASTED]]
; CHECK-NEXT: br i1 [[CMP]], label [[END:%.*]], label [[LOOP]]
; CHECK: loop:
; CHECK-NEXT: [[VAL_INCR:%.*]] = fadd float [[VAL_CASTED]], 1.000000e+00
; CHECK-NEXT: [[VAL_INCR_CASTED]] = bitcast float [[VAL_INCR]] to i32
; CHECK-NEXT: br label [[LOOP_HEADER]]
; CHECK: end:
; CHECK-NEXT: store volatile i32 [[VAL]], ptr @global, align 4
; CHECK-NEXT: ret void
;
entry:
br label %loop_header
loop_header:
%val = phi i32 [ 0, %entry ], [ %val_incr_casted, %loop ]
%val_casted = bitcast i32 %val to float
%cmp = fcmp ogt float %val_casted, %x
br i1 %cmp, label %end, label %loop
loop:
%val_incr = fadd float %val_casted, 1.0
%val_incr_casted = bitcast float %val_incr to i32
br label %loop_header
end:
store volatile i32 %val, ptr @global
ret void
}
; Use %val with a store where it's actually the address.
define void @store_address(i32 %x) {
; CHECK-LABEL: @store_address(
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[LOOP_HEADER:%.*]]
; CHECK: loop_header:
; CHECK-NEXT: [[VAL:%.*]] = phi ptr [ @global, [[ENTRY:%.*]] ], [ [[VAL_INCR:%.*]], [[LOOP:%.*]] ]
; CHECK-NEXT: [[CMP:%.*]] = icmp slt i32 [[X:%.*]], 0
; CHECK-NEXT: br i1 [[CMP]], label [[END:%.*]], label [[LOOP]]
; CHECK: loop:
; CHECK-NEXT: [[VAL_INCR]] = getelementptr i8, ptr [[VAL]], i64 4
; CHECK-NEXT: br label [[LOOP_HEADER]]
; CHECK: end:
; CHECK-NEXT: store i32 0, ptr [[VAL]], align 4
; CHECK-NEXT: ret void
;
entry:
br label %loop_header
loop_header:
%val = phi ptr [ @global, %entry ], [ %val_incr, %loop ]
%i = phi i32 [ 0, %entry ], [ %i_incr, %loop ]
%cmp = icmp sgt i32 %i, %x
br i1 %cmp, label %end, label %loop
loop:
%i_incr = add i32 %i, 0
%val_incr = getelementptr float, ptr %val, i32 1
br label %loop_header
end:
store i32 0, ptr %val
ret void
}
; Test where a phi (%val2) other than the original one (%val) has an
; incompatible use.
define i32 @multiple_phis(float %x) {
; CHECK-LABEL: @multiple_phis(
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[LOOP_HEADER:%.*]]
; CHECK: loop_header:
; CHECK-NEXT: [[VAL:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[VAL2:%.*]], [[LOOP_END:%.*]] ]
; CHECK-NEXT: [[VAL_CASTED:%.*]] = bitcast i32 [[VAL]] to float
; CHECK-NEXT: [[CMP:%.*]] = fcmp olt float [[X:%.*]], [[VAL_CASTED]]
; CHECK-NEXT: br i1 [[CMP]], label [[END:%.*]], label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[CMP2:%.*]] = fcmp ogt float [[VAL_CASTED]], 2.000000e+00
; CHECK-NEXT: br i1 [[CMP2]], label [[IF:%.*]], label [[LOOP_END]]
; CHECK: if:
; CHECK-NEXT: [[VAL_INCR:%.*]] = fadd float [[VAL_CASTED]], 1.000000e+00
; CHECK-NEXT: [[VAL_INCR_CASTED:%.*]] = bitcast float [[VAL_INCR]] to i32
; CHECK-NEXT: br label [[LOOP_END]]
; CHECK: loop_end:
; CHECK-NEXT: [[VAL2]] = phi i32 [ [[VAL]], [[LOOP]] ], [ [[VAL_INCR_CASTED]], [[IF]] ]
; CHECK-NEXT: store volatile i32 [[VAL2]], ptr @global, align 4
; CHECK-NEXT: br label [[LOOP_HEADER]]
; CHECK: end:
; CHECK-NEXT: ret i32 [[VAL]]
;
entry:
br label %loop_header
loop_header:
%val = phi i32 [ 0, %entry ], [ %val2, %loop_end ]
%val_casted = bitcast i32 %val to float
%cmp = fcmp ogt float %val_casted, %x
br i1 %cmp, label %end, label %loop
loop:
%cmp2 = fcmp ogt float %val_casted, 2.0
br i1 %cmp2, label %if, label %loop_end
if:
%val_incr = fadd float %val_casted, 1.0
%val_incr_casted = bitcast float %val_incr to i32
br label %loop_end
loop_end:
%val2 = phi i32 [ %val, %loop ], [ %val_incr_casted, %if ]
store volatile i32 %val2, ptr @global ; the incompatible use
br label %loop_header
end:
ret i32 %val
}
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