[Legalizer] Fix fp-to-uint to fp-tosint promotion assertion.
Summary:
When promoting fp-to-uint16 to fp-to-sint32, the result is actually zero
extended. For example, given double 65534.0, without legalization:
fp-to-uint16: 65534.0 -> 0xfffe
With the legalization:
fp-to-sint32: 65534.0 -> 0x0000fffe
Without this patch, legalization wrongly emits a signed extend assertion,
which is consumed by later icmp instruction, and cause miscompile.
Note that the floating point value must be in [0, 65535), otherwise the
behavior is undefined.
This patch reverts r279223 behavior and adds more tests and
documentations.
In PR29041's context, James Molloy mentioned that:
We don't need to mask because conversion from float->uint8_t is
undefined if the integer part of the float value is not representable in
uint8_t. Therefore we can assume this doesn't happen!
which is totally true and good, because fptoui is documented clearly to
have undefined behavior when overflow/underflow happens. We should take
the advantage of this behavior so that we can save unnecessary mask
instructions.
Reviewers: jmolloy, nadav, echristo, kbarton
Subscribers: mehdi_amini, nemanjai, llvm-commits
Differential Revision: https://reviews.llvm.org/D28284
llvm-svn: 291015
2017-01-05 06:11:42 +08:00
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; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
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; RUN: llc -O0 < %s | FileCheck %s
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target triple = "powerpc64le--linux-gnu"
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define i1 @Test(double %a) {
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; CHECK-LABEL: Test:
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; CHECK: # BB#0: # %entry
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; CHECK-NEXT: xscvdpsxws 1, 1
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; CHECK-NEXT: mfvsrwz 3, 1
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; CHECK-NEXT: xori 3, 3, 65534
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; CHECK-NEXT: cntlzw 3, 3
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; CHECK-NEXT: srwi 3, 3, 5
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2017-11-29 01:15:09 +08:00
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; CHECK-NEXT: # implicit-def: %x4
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[Legalizer] Fix fp-to-uint to fp-tosint promotion assertion.
Summary:
When promoting fp-to-uint16 to fp-to-sint32, the result is actually zero
extended. For example, given double 65534.0, without legalization:
fp-to-uint16: 65534.0 -> 0xfffe
With the legalization:
fp-to-sint32: 65534.0 -> 0x0000fffe
Without this patch, legalization wrongly emits a signed extend assertion,
which is consumed by later icmp instruction, and cause miscompile.
Note that the floating point value must be in [0, 65535), otherwise the
behavior is undefined.
This patch reverts r279223 behavior and adds more tests and
documentations.
In PR29041's context, James Molloy mentioned that:
We don't need to mask because conversion from float->uint8_t is
undefined if the integer part of the float value is not representable in
uint8_t. Therefore we can assume this doesn't happen!
which is totally true and good, because fptoui is documented clearly to
have undefined behavior when overflow/underflow happens. We should take
the advantage of this behavior so that we can save unnecessary mask
instructions.
Reviewers: jmolloy, nadav, echristo, kbarton
Subscribers: mehdi_amini, nemanjai, llvm-commits
Differential Revision: https://reviews.llvm.org/D28284
llvm-svn: 291015
2017-01-05 06:11:42 +08:00
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; CHECK-NEXT: mr 4, 3
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; CHECK-NEXT: mr 3, 4
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; CHECK-NEXT: blr
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entry:
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%conv = fptoui double %a to i16
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%cmp = icmp eq i16 %conv, -2
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ret i1 %cmp
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}
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