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Enhance address-mode folding of ISD::ADD to handle cases where the

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operands can't both be fully folded at the same time. For example,
in the included testcase, a global variable is being added with
an add of two values. The global variable wants RIP-relative
addressing, so it can't share the address with another base
register, but it's still possible to fold the initial add.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@66865 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman 2009-03-13 02:25:09 +00:00
parent 990afedb3a
commit 77502c9344
2 changed files with 38 additions and 0 deletions
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13
lib/Target/X86/X86ISelDAGToDAG.cpp
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@ -907,6 +907,19 @@ bool X86DAGToDAGISel::MatchAddress(SDValue N, X86ISelAddressMode &AM,
!MatchAddress(N.getNode()->getOperand(0), AM, false, Depth+1))
return false;
AM = Backup;
// If we couldn't fold both operands into the address at the same time,
// see if we can just put each operand into a register and fold at least
// the add.
if (AM.BaseType == X86ISelAddressMode::RegBase &&
!AM.Base.Reg.getNode() &&
!AM.IndexReg.getNode() &&
!AM.isRIPRel) {
AM.Base.Reg = N.getNode()->getOperand(0);
AM.IndexReg = N.getNode()->getOperand(1);
AM.Scale = 1;
return false;
}
break;
}

25
test/CodeGen/X86/fold-add.ll Normal file
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@ -0,0 +1,25 @@
; RUN: llvm-as < %s | llc -march=x86-64 | grep {cmpb \$0, (%r.\*,%r.\*)}
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128"
target triple = "x86_64-apple-darwin9.6"
@prev_length = internal global i32 0 ; <i32*> [#uses=1]
@window = internal global [65536 x i8] zeroinitializer, align 32 ; <[65536 x i8]*> [#uses=1]
@llvm.used = appending global [1 x i8*] [i8* bitcast (i32 (i32)* @longest_match to i8*)] ; <[1 x i8*]*> [#uses=0]
define fastcc i32 @longest_match(i32 %cur_match) nounwind {
entry:
%0 = load i32* @prev_length, align 4 ; <i32> [#uses=3]
%1 = zext i32 %cur_match to i64 ; <i64> [#uses=1]
%2 = sext i32 %0 to i64 ; <i64> [#uses=1]
%.sum3 = add i64 %1, %2 ; <i64> [#uses=1]
%3 = getelementptr [65536 x i8]* @window, i64 0, i64 %.sum3 ; <i8*> [#uses=1]
%4 = load i8* %3, align 1 ; <i8> [#uses=1]
%5 = icmp eq i8 %4, 0 ; <i1> [#uses=1]
br i1 %5, label %bb5, label %bb23
bb5: ; preds = %entry
ret i32 %0
bb23: ; preds = %entry
ret i32 %0
}