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X86: When lowering shl_parts, don't emit shift amounts larger than the bit width.

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While it's safe for the X86-specific shift nodes, dag combining will
kill generic nodes. Insert an AND to make it safe, isel will nuke it
as x86's shift instructions have an implicit AND.

Fixes PR16108, which contains a contraption to hit this case in between
constant folders.

llvm-svn: 197228
This commit is contained in:
Benjamin Kramer 2013-12-13 13:40:24 +00:00
parent 2826f5b278
commit 123ebfd785
2 changed files with 38 additions and 2 deletions
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12
lib/Target/X86/X86ISelLowering.cpp
View File

@ -8459,6 +8459,11 @@ SDValue X86TargetLowering::LowerShiftParts(SDValue Op, SelectionDAG &DAG) const{
SDValue ShOpLo = Op.getOperand(0);
SDValue ShOpHi = Op.getOperand(1);
SDValue ShAmt = Op.getOperand(2);
// X86ISD::SHLD and X86ISD::SHRD have defined overflow behavior but the
// generic ISD nodes haven't. Insert an AND to be safe, it's optimized away
// during isel.
SDValue SafeShAmt = DAG.getNode(ISD::AND, dl, MVT::i8, ShAmt,
DAG.getConstant(VTBits - 1, MVT::i8));
SDValue Tmp1 = isSRA ? DAG.getNode(ISD::SRA, dl, VT, ShOpHi,
DAG.getConstant(VTBits - 1, MVT::i8))
: DAG.getConstant(0, VT);
@ -8466,12 +8471,15 @@ SDValue X86TargetLowering::LowerShiftParts(SDValue Op, SelectionDAG &DAG) const{
SDValue Tmp2, Tmp3;
if (Op.getOpcode() == ISD::SHL_PARTS) {
Tmp2 = DAG.getNode(X86ISD::SHLD, dl, VT, ShOpHi, ShOpLo, ShAmt);
Tmp3 = DAG.getNode(ISD::SHL, dl, VT, ShOpLo, ShAmt);
Tmp3 = DAG.getNode(ISD::SHL, dl, VT, ShOpLo, SafeShAmt);
} else {
Tmp2 = DAG.getNode(X86ISD::SHRD, dl, VT, ShOpLo, ShOpHi, ShAmt);
Tmp3 = DAG.getNode(isSRA ? ISD::SRA : ISD::SRL, dl, VT, ShOpHi, ShAmt);
Tmp3 = DAG.getNode(isSRA ? ISD::SRA : ISD::SRL, dl, VT, ShOpHi, SafeShAmt);
}
// If the shift amount is larger or equal than the width of a part we can't
// rely on the results of shld/shrd. Insert a test and select the appropriate
// values for large shift amounts.
SDValue AndNode = DAG.getNode(ISD::AND, dl, MVT::i8, ShAmt,
DAG.getConstant(VTBits, MVT::i8));
SDValue Cond = DAG.getNode(X86ISD::CMP, dl, MVT::i32,

28
test/CodeGen/X86/legalize-shift-64.ll
View File

@ -64,3 +64,31 @@ define <2 x i64> @test5(<2 x i64> %A, <2 x i64> %B) {
; CHECK: shl
; CHECK: shldl
}
; PR16108
define i32 @test6() {
%x = alloca i32, align 4
%t = alloca i64, align 8
store i32 1, i32* %x, align 4
store i64 1, i64* %t, align 8 ;; DEAD
%load = load i32* %x, align 4
%shl = shl i32 %load, 8
%add = add i32 %shl, -224
%sh_prom = zext i32 %add to i64
%shl1 = shl i64 1, %sh_prom
%cmp = icmp ne i64 %shl1, 4294967296
br i1 %cmp, label %if.then, label %if.end
if.then: ; preds = %entry
ret i32 1
if.end: ; preds = %entry
ret i32 0
; CHECK-LABEL: test6:
; CHECK-NOT: andb $31
; CHECK: sete
; CHECK: movzbl
; CHECK: xorl $1
; CHECK: orl
}