[llvm] r293025 - [SimplifyCFG] Do not sink and merge inline-asm instructions.

[Akira Hatanaka via llvm-commits]

Author: ahatanak
Date: Wed Jan 25 00:21:51 2017
New Revision: 293025

URL: http://llvm.org/viewvc/llvm-project?rev=293025&view=rev
Log:
[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




Modified:
    llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
    llvm/trunk/test/Transforms/SimplifyCFG/sink-common-code.ll

Modified: llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp?rev=293025&r1=293024&r2=293025&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp Wed Jan 25 00:21:51 2017
@@ -1436,6 +1436,14 @@ static bool canSinkInstructions(
     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())

Modified: llvm/trunk/test/Transforms/SimplifyCFG/sink-common-code.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SimplifyCFG/sink-common-code.ll?rev=293025&r1=293024&r2=293025&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/SimplifyCFG/sink-common-code.ll (original)
+++ llvm/trunk/test/Transforms/SimplifyCFG/sink-common-code.ll Wed Jan 25 00:21:51 2017
@@ -768,6 +768,30 @@ if.end:
 ; CHECK-NOT: exact
 ; CHECK: }
 
+; Check that simplifycfg doesn't sink and merge inline-asm instructions.
+
+define i32 @test_inline_asm1(i32 %c, i32 %r6) {
+entry:
+  %tobool = icmp eq i32 %c, 0
+  br i1 %tobool, label %if.else, label %if.then
+
+if.then:
+  %0 = call i32 asm "rorl $2, $0", "=&r,0,n,~{dirflag},~{fpsr},~{flags}"(i32 %r6, i32 8)
+  br label %if.end
+
+if.else:
+  %1 = call i32 asm "rorl $2, $0", "=&r,0,n,~{dirflag},~{fpsr},~{flags}"(i32 %r6, i32 6)
+  br label %if.end
+
+if.end:
+  %r6.addr.0 = phi i32 [ %0, %if.then ], [ %1, %if.else ]
+  ret i32 %r6.addr.0
+}
+
+; CHECK-LABEL: @test_inline_asm1(
+; CHECK: call i32 asm "rorl $2, $0", "=&r,0,n,~{dirflag},~{fpsr},~{flags}"(i32 %r6, i32 8)
+; CHECK: call i32 asm "rorl $2, $0", "=&r,0,n,~{dirflag},~{fpsr},~{flags}"(i32 %r6, i32 6)
+
 declare i32 @call_target()
 
 define void @test_operand_bundles(i1 %cond, i32* %ptr) {