From 53f4c4b2cc51f4848dfc610a3a858ef821e39ae5 Mon Sep 17 00:00:00 2001
From: Florian Hahn <flo@fhahn.com>
Date: Wed, 28 Oct 2020 21:49:33 +0000
Subject: [PATCH] [InstCombine] Do not introduce bitcasts for swifterror
 arguments.

The following constraints hold for swifterror values:

    A swifterror value (either the parameter or the alloca) can only
    be loaded and stored from, or used as a swifterror argument.

This patch updates instcombine to not try to convert a bitcast of a
function into a bitcast of a swifterror argument.

Reviewed By: rjmccall

Differential Revision: https://reviews.llvm.org/D90258
---
 llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp   |  3 +++
 .../InstCombine/swifterror-argument-bitcast-fold.ll    | 18 ++++++++++++++++++
 2 files changed, 21 insertions(+)
 create mode 100644 llvm/test/Transforms/InstCombine/swifterror-argument-bitcast-fold.ll

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index c069657..3b0b12d 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -2126,6 +2126,9 @@ bool InstCombinerImpl::transformConstExprCastCall(CallBase &Call) {
     if (Call.isInAllocaArgument(i))
       return false;   // Cannot transform to and from inalloca.
 
+    if (CallerPAL.hasParamAttribute(i, Attribute::SwiftError))
+      return false;
+
     // If the parameter is passed as a byval argument, then we have to have a
     // sized type and the sized type has to have the same size as the old type.
     if (ParamTy != ActTy && CallerPAL.hasParamAttribute(i, Attribute::ByVal)) {
diff --git a/llvm/test/Transforms/InstCombine/swifterror-argument-bitcast-fold.ll b/llvm/test/Transforms/InstCombine/swifterror-argument-bitcast-fold.ll
new file mode 100644
index 0000000..22a98f3
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/swifterror-argument-bitcast-fold.ll
@@ -0,0 +1,18 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -instcombine -S %s | FileCheck %s
+
+; The swifterror value can only be loaded, stored or used as swifterror
+; argument. Make sure we do not try to turn the function bitcast into an
+; argument bitcast.
+define swiftcc void @spam(i32** swifterror %arg) {
+; CHECK-LABEL: @spam(
+; CHECK-NEXT:  bb:
+; CHECK-NEXT:    call swiftcc void bitcast (void (i64**)* @widget to void (i32**)*)(i32** swifterror [[ARG:%.*]])
+; CHECK-NEXT:    ret void
+;
+bb:
+  call swiftcc void bitcast (void (i64**)* @widget to void (i32**)*)(i32** swifterror %arg)
+  ret void
+}
+
+declare swiftcc void @widget(i64**)
-- 
2.7.4