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author | Benjamin Kramer <benny.kra@googlemail.com> | 2011-04-22 18:47:44 +0000 |
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committer | Benjamin Kramer <benny.kra@googlemail.com> | 2011-04-22 18:47:44 +0000 |
commit | e7cf062537e898f830565db5dbf99ae9c928399e (patch) | |
tree | 3c87d0506e38a3039f8e6df7fc0ed061d232dd8c /lib | |
parent | eac0c9dc7759b013bbe831ace1afa37bc46915c6 (diff) | |
download | llvm-e7cf062537e898f830565db5dbf99ae9c928399e.tar.gz llvm-e7cf062537e898f830565db5dbf99ae9c928399e.tar.bz2 llvm-e7cf062537e898f830565db5dbf99ae9c928399e.tar.xz |
DAGCombine: fold "(zext x) == C" into "x == (trunc C)" if the trunc is lossless.
On x86 this allows to fold a load into the cmp, greatly reducing register pressure.
movzbl (%rdi), %eax
cmpl $47, %eax
->
cmpb $47, (%rdi)
This shaves 8k off gcc.o on i386. I'll leave applying the patch in README.txt to Chris :)
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@130005 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib')
-rw-r--r-- | lib/CodeGen/SelectionDAG/TargetLowering.cpp | 36 | ||||
-rw-r--r-- | lib/Target/README.txt | 31 |
2 files changed, 37 insertions, 30 deletions
diff --git a/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/lib/CodeGen/SelectionDAG/TargetLowering.cpp index 843ed96cba..15606af787 100644 --- a/lib/CodeGen/SelectionDAG/TargetLowering.cpp +++ b/lib/CodeGen/SelectionDAG/TargetLowering.cpp @@ -1916,6 +1916,42 @@ TargetLowering::SimplifySetCC(EVT VT, SDValue N0, SDValue N1, // TODO: (ctpop x) == 1 -> x && (x & x-1) == 0 iff ctpop is illegal. } + // (zext x) == C --> x == (trunc C) + if (DCI.isBeforeLegalize() && N0->hasOneUse() && + (Cond == ISD::SETEQ || Cond == ISD::SETNE)) { + unsigned MinBits = N0.getValueSizeInBits(); + SDValue PreZExt; + if (N0->getOpcode() == ISD::ZERO_EXTEND) { + // ZExt + MinBits = N0->getOperand(0).getValueSizeInBits(); + PreZExt = N0->getOperand(0); + } else if (N0->getOpcode() == ISD::AND) { + // DAGCombine turns costly ZExts into ANDs + if (ConstantSDNode *C = dyn_cast<ConstantSDNode>(N0->getOperand(1))) + if ((C->getAPIntValue()+1).isPowerOf2()) { + MinBits = C->getAPIntValue().countTrailingOnes(); + PreZExt = N0->getOperand(0); + } + } else if (LoadSDNode *LN0 = dyn_cast<LoadSDNode>(N0)) { + // ZEXTLOAD + if (LN0->getExtensionType() == ISD::ZEXTLOAD) { + MinBits = LN0->getMemoryVT().getSizeInBits(); + PreZExt = N0; + } + } + + // Make sure we're not loosing bits from the constant. + if (MinBits < C1.getBitWidth() && MinBits > C1.getActiveBits()) { + EVT MinVT = EVT::getIntegerVT(*DAG.getContext(), MinBits); + if (isTypeDesirableForOp(ISD::SETCC, MinVT)) { + // Will get folded away. + SDValue Trunc = DAG.getNode(ISD::TRUNCATE, dl, MinVT, PreZExt); + SDValue C = DAG.getConstant(C1.trunc(MinBits), MinVT); + return DAG.getSetCC(dl, VT, Trunc, C, Cond); + } + } + } + // If the LHS is '(and load, const)', the RHS is 0, // the test is for equality or unsigned, and all 1 bits of the const are // in the same partial word, see if we can shorten the load. diff --git a/lib/Target/README.txt b/lib/Target/README.txt index 5032b2bbbb..c345ce50c0 100644 --- a/lib/Target/README.txt +++ b/lib/Target/README.txt @@ -2259,34 +2259,6 @@ icmp transform. //===---------------------------------------------------------------------===// -These functions: -int foo(int *X) { - if ((*X & 255) == 47) - bar(); -} -int foo2(int X) { - if ((X & 255) == 47) - bar(); -} - -codegen to: - - movzbl (%rdi), %eax - cmpl $47, %eax - jne LBB0_2 - -and: - movzbl %dil, %eax - cmpl $47, %eax - jne LBB1_2 - -If a dag combine shrunk the compare to a byte compare, then we'd fold the load -in the first example, and eliminate the movzbl in the second, saving a register. -This can be a target independent dag combine that works on ISD::SETCC, it would -catch this before the legalize ops pass. - -//===---------------------------------------------------------------------===// - We should optimize this: %tmp = load i16* %arrayidx, align 4, !tbaa !0 @@ -2329,8 +2301,7 @@ Index: InstCombine/InstCombineCompares.cpp { -but we can't do that until the dag combine above is added. Not having this -is blocking resolving PR6627. +Not having this is blocking resolving PR6627. //===---------------------------------------------------------------------===// |