Merging r197228:

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r197228 | d0k | 2013-12-13 05:40:24 -0800 (Fri, 13 Dec 2013) | 8 lines

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

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.
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_34@197321 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index 12d40c488ada69000de4a6c53229b969e6542003..d0667ff54a4858b0124da4ac60eb920427e36e15 100644 (file)
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -8424,6 +8424,11 @@ 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);
@@ -8431,12 +8436,15 @@ 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,

diff --git a/test/CodeGen/X86/legalize-shift-64.ll b/test/CodeGen/X86/legalize-shift-64.ll
index 77364688afe4391360e92c8163a8beec46123249..64460bb91186c6bc5403b226b7a5aeabf68cc0c8 100644 (file)
--- a/test/CodeGen/X86/legalize-shift-64.ll
+++ b/test/CodeGen/X86/legalize-shift-64.ll
@@ -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
+}