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author | Chris Lattner <sabre@nondot.org> | 2011-04-26 20:18:20 +0000 |
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committer | Chris Lattner <sabre@nondot.org> | 2011-04-26 20:18:20 +0000 |
commit | 325eeb1cd7c3247ead1513204bc9cf4b6e883653 (patch) | |
tree | 4e02166fa21871f7f77097284b7f1e5aba28af3c /lib/Target/README.txt | |
parent | 5036ce4a64caaeaff4b1f8f1c91836cc2e49a455 (diff) | |
download | llvm-325eeb1cd7c3247ead1513204bc9cf4b6e883653.tar.gz llvm-325eeb1cd7c3247ead1513204bc9cf4b6e883653.tar.bz2 llvm-325eeb1cd7c3247ead1513204bc9cf4b6e883653.tar.xz |
Transform: "icmp eq (trunc (lshr(X, cst1)), cst" to "icmp (and X, mask), cst"
when X has multiple uses. This is useful for exposing secondary optimizations,
but the X86 backend isn't ready for this when X has a single use. For example,
this can disable load folding.
This is inching towards resolving PR6627.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@130238 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib/Target/README.txt')
-rw-r--r-- | lib/Target/README.txt | 46 |
1 files changed, 0 insertions, 46 deletions
diff --git a/lib/Target/README.txt b/lib/Target/README.txt index 99e1252dc8..ffe3fa477b 100644 --- a/lib/Target/README.txt +++ b/lib/Target/README.txt @@ -2259,52 +2259,6 @@ icmp transform. //===---------------------------------------------------------------------===// -We should optimize this: - - %tmp = load i16* %arrayidx, align 4, !tbaa !0 - %A = trunc i16 %tmp to i8 - %cmp = icmp eq i8 %A, 127 - %B.mask = and i16 %tmp, -256 - %cmp7 = icmp eq i16 %B.mask, 17664 - %or.cond = and i1 %cmp, %cmp7 - br i1 %or.cond, label %land.lhs.true9, label %if.end - -into: - - %tmp = load i16* %arrayidx, align 4, !tbaa !0 - %0 = icmp eq i16 %tmp, 17791 - br i1 %0, label %land.lhs.true9, label %if.end - -with this patch: -Index: InstCombine/InstCombineCompares.cpp -=================================================================== ---- InstCombine/InstCombineCompares.cpp (revision 129500) -+++ InstCombine/InstCombineCompares.cpp (working copy) -@@ -2506,6 +2506,18 @@ - return &I; - } - } -+ -+ // Transform "icmp eq (trunc X), cst" to "icmp (and X, mask), cst" -+ if (Op0->hasOneUse() && match(Op0, m_Trunc(m_Value(A))) && -+ isa<ConstantInt>(Op1)) { -+ APInt MaskV = APInt::getLowBitsSet(A->getType()->getPrimitiveSizeInBits(), -+ Op0->getType()->getPrimitiveSizeInBits()); -+ Value *Mask = -+ Builder->CreateAnd(A, ConstantInt::get(A->getContext(), MaskV)); -+ return new ICmpInst(I.getPredicate(), Mask, -+ ConstantExpr::getZExt(cast<ConstantInt>(Op1), -+ Mask->getType())); -+ } - } - - { - - -Not having this is blocking resolving PR6627. - -//===---------------------------------------------------------------------===// - This code: typedef struct { |