From 02e92a0b5dd75514c8489d3f87fe7c5262ca6290 Mon Sep 17 00:00:00 2001
From: Chandler Carruth <chandlerc@gmail.com>
Date: Sun, 23 Sep 2012 11:43:14 +0000
Subject: Switch to a signed representation for the dynamic offsets while
 walking across the uses of the alloca. It's entirely possible for negative
 numbers to come up here, and in some rare cases simply doing the 2's
 complement arithmetic isn't the correct decision. Notably, we can't zext the
 index of the GEP. The definition of GEP is that these offsets are sign
 extended or truncated to the size of the pointer, and then wrapping 2's
 complement arithmetic used.

This patch fixes an issue that comes up with *no* input from the
buildbots or bootstrap afaict. The only place where it manifested,
disturbingly, is Clang's own regression test suite. A reduced and
targeted collection of tests are added to cope with this. Note that I've
tried to pin down the potential cases of overflow, but may have missed
some cases. I've tried to add a few cases to test this, but its hard
because LLVM has quite limited support for >64bit constructs.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@164475 91177308-0d34-0410-b5e6-96231b3b80d8
---
 test/Transforms/SROA/basictest.ll | 58 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 58 insertions(+)

(limited to 'test/Transforms/SROA')

diff --git a/test/Transforms/SROA/basictest.ll b/test/Transforms/SROA/basictest.ll
index 82c524d..be3ef64 100644
--- a/test/Transforms/SROA/basictest.ll
+++ b/test/Transforms/SROA/basictest.ll
@@ -774,3 +774,61 @@ entry:
   %val = load i64* %gep
   ret i32 undef
 }
+
+define i32 @test20() {
+; Ensure we can track negative offsets (before the beginning of the alloca) and
+; negative relative offsets from offsets starting past the end of the alloca.
+; CHECK: @test20
+; CHECK-NOT: alloca
+; CHECK: %[[sum1:.*]] = add i32 1, 2
+; CHECK: %[[sum2:.*]] = add i32 %[[sum1]], 3
+; CHECK: ret i32 %[[sum2]]
+
+entry:
+  %a = alloca [3 x i32]
+  %gep1 = getelementptr [3 x i32]* %a, i32 0, i32 0
+  store i32 1, i32* %gep1
+  %gep2.1 = getelementptr [3 x i32]* %a, i32 0, i32 -2
+  %gep2.2 = getelementptr i32* %gep2.1, i32 3
+  store i32 2, i32* %gep2.2
+  %gep3.1 = getelementptr [3 x i32]* %a, i32 0, i32 14
+  %gep3.2 = getelementptr i32* %gep3.1, i32 -12
+  store i32 3, i32* %gep3.2
+
+  %load1 = load i32* %gep1
+  %load2 = load i32* %gep2.2
+  %load3 = load i32* %gep3.2
+  %sum1 = add i32 %load1, %load2
+  %sum2 = add i32 %sum1, %load3
+  ret i32 %sum2
+}
+
+declare void @llvm.memset.p0i8.i64(i8* nocapture, i8, i64, i32, i1) nounwind
+
+define i8 @test21() {
+; Test allocations and offsets which border on overflow of the int64_t used
+; internally. This is really awkward to really test as LLVM doesn't really
+; support such extreme constructs cleanly.
+; CHECK: @test21
+; CHECK-NOT: alloca
+; CHECK: or i8 -1, -1
+
+entry:
+  %a = alloca [2305843009213693951 x i8]
+  %gep0 = getelementptr [2305843009213693951 x i8]* %a, i64 0, i64 2305843009213693949
+  store i8 255, i8* %gep0
+  %gep1 = getelementptr [2305843009213693951 x i8]* %a, i64 0, i64 -9223372036854775807
+  %gep2 = getelementptr i8* %gep1, i64 -1
+  call void @llvm.memset.p0i8.i64(i8* %gep2, i8 0, i64 18446744073709551615, i32 1, i1 false)
+  %gep3 = getelementptr i8* %gep1, i64 9223372036854775807
+  %gep4 = getelementptr i8* %gep3, i64 9223372036854775807
+  %gep5 = getelementptr i8* %gep4, i64 -6917529027641081857
+  store i8 255, i8* %gep5
+  %cast1 = bitcast i8* %gep4 to i32*
+  store i32 0, i32* %cast1
+  %load = load i8* %gep0
+  %gep6 = getelementptr i8* %gep0, i32 1
+  %load2 = load i8* %gep6
+  %result = or i8 %load, %load2
+  ret i8 %result
+}
-- 
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