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[ARM] Fix 28282: cost computation for constant hoisting

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Summary:
This fixes bug: https://llvm.org/bugs/show_bug.cgi?id=28282

Currently the cost model of constant hoisting checks the bit width of the data type of the constants.
However, the actual immediate value is small enough and not need to be hoisted.
This patch checks for the actual bit width needed for the constant.

Reviewers: t.p.northover, rengolin

Subscribers: aemerson, rengolin, llvm-commits

Differential Revision: http://reviews.llvm.org/D21668

llvm-svn: 274073
This commit is contained in:
Weiming Zhao 2016-06-28 22:30:45 +00:00
parent 4ffa29a4fb
commit 011d429eab
2 changed files with 18 additions and 1 deletions
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2
lib/Target/ARM/ARMTargetTransformInfo.cpp
View File

@ -19,7 +19,7 @@ int ARMTTIImpl::getIntImmCost(const APInt &Imm, Type *Ty) {
assert(Ty->isIntegerTy());
unsigned Bits = Ty->getPrimitiveSizeInBits();
if (Bits == 0 || Bits > 64)
if (Bits == 0 || Imm.getActiveBits() >= 64)
return 4;
int64_t SImmVal = Imm.getSExtValue();

17
test/Transforms/ConstantHoisting/ARM/bad-cases.ll
View File

@ -90,3 +90,20 @@ loop:
end:
ret void
}
;PR 28282: even when data type is larger than 64-bit, the bit width of the
;constant operand could be smaller than 64-bit. In this case, there is no
;benefit to hoist the constant.
define i32 @struct_type_test(i96 %a0, i96 %a1) {
;CHECK-LABEL: @struct_type_test
entry:
;CHECK-NOT: %const = bitcast i96 32 to i96
;CHECK: lshr0 = lshr i96 %a0, 32
%lshr0 = lshr i96 %a0, 32
%cast0 = trunc i96 %lshr0 to i32
;CHECK: lshr1 = lshr i96 %a1, 32
%lshr1 = lshr i96 %a1, 32
%cast1 = trunc i96 %lshr1 to i32
%ret = add i32 %cast0, %cast1
ret i32 %ret
}