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[InstCombine] conditional sign-extend of high-bit-extract: 'or' pattern.

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In this pattern, all the "magic" bits that we'd `add` are all
high sign bits, and in the value we'd be adding to they are all unset,
not unexpectedly, so we can have an `or` there:
https://rise4fun.com/Alive/ups

It is possible that `haveNoCommonBitsSet()` should be taught about this
pattern so that we never have an `add` variant, but the reasoning would
need to be recursive (because of that `select`), so i'm not really sure
that would be worth it just yet.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@375378 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Roman Lebedev
2019-10-20 20:52:06 +00:00
parent 150b0bedb7
commit b93a52f5fe
4 changed files with 26 additions and 21 deletions
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test/Transforms/InstCombine/conditional-variable-length-signext-after-high-bit-extract.ll
+3 -3
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@@ -57,7 +57,7 @@ define i32 @t0_notrunc_or(i32 %data, i32 %nbits) {
; CHECK-NEXT: call void @use1(i1 [[SHOULD_SIGNEXT]])
; CHECK-NEXT: call void @use32(i32 [[ALL_BITS_EXCEPT_LOW_NBITS]])
; CHECK-NEXT: call void @use32(i32 [[MAGIC]])
; CHECK-NEXT: [[SIGNEXTENDED:%.*]] = or i32 [[HIGH_BITS_EXTRACTED]], [[MAGIC]]
; CHECK-NEXT: [[SIGNEXTENDED:%.*]] = ashr i32 [[DATA]], [[LOW_BITS_TO_SKIP]]
; CHECK-NEXT: ret i32 [[SIGNEXTENDED]]
;
%low_bits_to_skip = sub i32 32, %nbits
@@ -152,14 +152,14 @@ define i32 @t2_trunc_or(i64 %data, i32 %nbits) {
; CHECK-NEXT: [[HIGH_BITS_EXTRACTED:%.*]] = trunc i64 [[HIGH_BITS_EXTRACTED_WIDE]] to i32
; CHECK-NEXT: [[SHOULD_SIGNEXT:%.*]] = icmp slt i64 [[DATA]], 0
; CHECK-NEXT: [[ALL_BITS_EXCEPT_LOW_NBITS:%.*]] = shl i32 -1, [[NBITS]]
; CHECK-NEXT: [[MAGIC:%.*]] = select i1 [[SHOULD_SIGNEXT]], i32 [[ALL_BITS_EXCEPT_LOW_NBITS]], i32 0
; CHECK-NEXT: call void @use32(i32 [[LOW_BITS_TO_SKIP]])
; CHECK-NEXT: call void @use64(i64 [[LOW_BITS_TO_SKIP_WIDE]])
; CHECK-NEXT: call void @use64(i64 [[HIGH_BITS_EXTRACTED_WIDE]])
; CHECK-NEXT: call void @use32(i32 [[HIGH_BITS_EXTRACTED]])
; CHECK-NEXT: call void @use1(i1 [[SHOULD_SIGNEXT]])
; CHECK-NEXT: call void @use32(i32 [[ALL_BITS_EXCEPT_LOW_NBITS]])
; CHECK-NEXT: [[SIGNEXTENDED:%.*]] = or i32 [[MAGIC]], [[HIGH_BITS_EXTRACTED]]
; CHECK-NEXT: [[TMP1:%.*]] = ashr i64 [[DATA]], [[LOW_BITS_TO_SKIP_WIDE]]
; CHECK-NEXT: [[SIGNEXTENDED:%.*]] = trunc i64 [[TMP1]] to i32
; CHECK-NEXT: ret i32 [[SIGNEXTENDED]]
;
%low_bits_to_skip = sub i32 64, %nbits