[SimplifyCFG] Do not sink and merge inline-asm instructions.
Conservatively disable sinking and merging inline-asm instructions as doing so
can potentially create arguments that cannot satisfy the inline-asm constraints.
For example, SimplifyCFG used to do the following transformation:
(before)
if.then:
%0 = call i32 asm "rorl $2, $0", "=&r,0,n"(i32 %r6, i32 8)
br label %if.end
if.else:
%1 = call i32 asm "rorl $2, $0", "=&r,0,n"(i32 %r6, i32 6)
br label %if.end
(after)
%.sink = select i1 %tobool, i32 6, i32 8
%0 = call i32 asm "rorl $2, $0", "=&r,0,n"(i32 %r6, i32 %.sink)
This would result in a crash in the backend since only immediate integer operands
are permitted for constraint "n".
rdar://problem/30110806
Differential Revision: https://reviews.llvm.org/D29111
llvm-svn: 293025
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index cb1492f..e287916 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -1436,6 +1436,14 @@
if (isa<PHINode>(I) || I->isEHPad() || isa<AllocaInst>(I) ||
I->getType()->isTokenTy())
return false;
+
+ // Conservatively return false if I is an inline-asm instruction. Sinking
+ // and merging inline-asm instructions can potentially create arguments
+ // that cannot satisfy the inline-asm constraints.
+ if (const auto *C = dyn_cast<CallInst>(I))
+ if (C->isInlineAsm())
+ return false;
+
// Everything must have only one use too, apart from stores which
// have no uses.
if (!isa<StoreInst>(I) && !I->hasOneUse())