[ARM] Skip inline asm memory operands in DAGToDAGISel

The current logic for handling inline asm operands in DAGToDAGISel interprets
the operands by looking for constants, which should represent the flags
describing the kind of operand we're dealing with (immediate, memory, register
def etc). The operands representing actual data are skipped only if they are
non-const, with the exception of immediate operands which are skipped explicitly
when a flag describing an immediate is found.

The oversight is that memory operands may be const too (e.g. for device drivers
reading a fixed address), so we should explicitly skip the operand following a
flag describing a memory operand. If we don't, we risk interpreting that
constant as a flag, which is definitely not intended.

Fixes PR26038

Differential Revision: https://reviews.llvm.org/D22103

llvm-svn: 275776

2 files changed, 22 insertions, 0 deletions

diff --git a/llvm/lib/Target/ARM/ARMISelDAGToDAG.cpp b/llvm/lib/Target/ARM/ARMISelDAGToDAG.cpp
index c5e1d976bbb..20db3d39bca 100644
--- a/llvm/lib/Target/ARM/ARMISelDAGToDAG.cpp
+++ b/llvm/lib/Target/ARM/ARMISelDAGToDAG.cpp
@@ -4264,6 +4264,17 @@ bool ARMDAGToDAGISel::tryInlineAsm(SDNode *N){
     if (Changed && InlineAsm::isUseOperandTiedToDef(Flag, DefIdx))
       IsTiedToChangedOp = OpChanged[DefIdx];
 
+    // Memory operands to inline asm in the SelectionDAG are modeled with two
+    // operands: a constant of value InlineAsm::Kind_Mem followed by the input
+    // operand. If we get here and we have a Kind_Mem, skip the next operand (so
+    // it doesn't get misinterpreted), and continue. We do this here because
+    // it's important to update the OpChanged array correctly before moving on.
+    if (Kind == InlineAsm::Kind_Mem) {
+      SDValue op = N->getOperand(++i);
+      AsmNodeOperands.push_back(op);
+      continue;
+    }
+
     if (Kind != InlineAsm::Kind_RegUse && Kind != InlineAsm::Kind_RegDef
         && Kind != InlineAsm::Kind_RegDefEarlyClobber)
       continue;
diff --git a/llvm/test/CodeGen/ARM/inlineasm3.ll b/llvm/test/CodeGen/ARM/inlineasm3.ll
index eb7ba59b69b..59706c4e418 100644
--- a/llvm/test/CodeGen/ARM/inlineasm3.ll
+++ b/llvm/test/CodeGen/ARM/inlineasm3.ll
@@ -121,3 +121,14 @@ entry:
   %0 = tail call <4 x i32> asm "vld1.s32 {${0:e}[], ${0:f}[]}, [$1]", "=w,r"(i32* %p) nounwind
   ret <4 x i32> %0
 }
+
+; Bugzilla PR26038
+
+define i32 @fn1() local_unnamed_addr nounwind {
+; CHECK-LABEL: fn1
+entry:
+; CHECK: mov [[addr:r[0-9]+]], #5
+; CHECK: ldrh {{.*}}[[addr]]
+  %0 = tail call i32 asm "ldrh  $0, $1", "=r,*Q"(i8* inttoptr (i32 5 to i8*)) nounwind
+  ret i32 %0
+}