Implementation of asm-goto support in LLVM

This patch accompanies the RFC posted here:
http://lists.llvm.org/pipermail/llvm-dev/2018-October/127239.html

This patch adds a new CallBr IR instruction to support asm-goto
inline assembly like gcc as used by the linux kernel. This
instruction is both a call instruction and a terminator
instruction with multiple successors. Only inline assembly
usage is supported today.

This also adds a new INLINEASM_BR opcode to SelectionDAG and
MachineIR to represent an INLINEASM block that is also
considered a terminator instruction.

There will likely be more bug fixes and optimizations to follow
this, but we felt it had reached a point where we would like to
switch to an incremental development model.

Patch by Craig Topper, Alexander Ivchenko, Mikhail Dvoretckii

Differential Revision: https://reviews.llvm.org/D53765

llvm-svn: 353563

1 files changed, 3 insertions, 5 deletions

diff --git a/llvm/lib/CodeGen/IndirectBrExpandPass.cpp b/llvm/lib/CodeGen/IndirectBrExpandPass.cpp
index 9a96abfbf8c..7ac093ba4a7 100644
--- a/llvm/lib/CodeGen/IndirectBrExpandPass.cpp
+++ b/llvm/lib/CodeGen/IndirectBrExpandPass.cpp
@@ -148,11 +148,9 @@ bool IndirectBrExpandPass::runOnFunction(Function &F) {
     ConstantInt *BBIndexC = ConstantInt::get(ITy, BBIndex);
 
     // Now rewrite the blockaddress to an integer constant based on the index.
-    // FIXME: We could potentially preserve the uses as arguments to inline asm.
-    // This would allow some uses such as diagnostic information in crashes to
-    // have higher quality even when this transform is enabled, but would break
-    // users that round-trip blockaddresses through inline assembly and then
-    // back into an indirectbr.
+    // FIXME: This part doesn't properly recognize other uses of blockaddress
+    // expressions, for instance, where they are used to pass labels to
+    // asm-goto. This part of the pass needs a rework.
     BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(BBIndexC, BA->getType()));
   }