teach libanalysis to fold int and fp loads from almost arbitrary

non-type-safe constant initializers.  This sort of thing happens
quite a bit for 4-byte loads out of string constants, unions, 
bitfields, and an interesting endianness check from sqlite, which
is something like this:

const int sqlite3one = 1;
# define SQLITE_BIGENDIAN    (*(char *)(&sqlite3one)==0)
# define SQLITE_LITTLEENDIAN (*(char *)(&sqlite3one)==1)
# define SQLITE_UTF16NATIVE (SQLITE_BIGENDIAN?SQLITE_UTF16BE:SQLITE_UTF16LE)

all of these macros now constant fold away.

This implements PR3152 and is based on a patch started by Eli, but heavily
modified and extended.

llvm-svn: 84936

1 files changed, 68 insertions, 0 deletions

diff --git a/llvm/test/Transforms/ConstProp/loads.ll b/llvm/test/Transforms/ConstProp/loads.ll
new file mode 100644
index 00000000000..f3633cc4438
--- /dev/null
+++ b/llvm/test/Transforms/ConstProp/loads.ll
@@ -0,0 +1,68 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s 
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128"
+
+@test1 = constant {{i32,i8},i32} {{i32,i8} { i32 -559038737, i8 186 }, i32 -889275714 }
+@test2 = constant double 1.0
+
+; Simple load
+define i32 @test1() {
+  %r = load i32* getelementptr ({{i32,i8},i32}* @test1, i32 0, i32 0, i32 0)
+  ret i32 %r
+; @test1
+; CHECK: ret i32 -559038737
+}
+
+; PR3152
+; Load of first 16 bits of 32-bit value.
+define i16 @test2() {
+  %r = load i16* bitcast(i32* getelementptr ({{i32,i8},i32}* @test1, i32 0, i32 0, i32 0) to i16*)
+  ret i16 %r
+
+; @test2
+; CHECK: ret i16 -16657 
+}
+
+; Load of second 16 bits of 32-bit value.
+define i16 @test3() {
+  %r = load i16* getelementptr(i16* bitcast(i32* getelementptr ({{i32,i8},i32}* @test1, i32 0, i32 0, i32 0) to i16*), i32 1)
+  ret i16 %r
+
+; @test3
+; CHECK: ret i16 -8531
+}
+
+; Load of 8 bit field + tail padding.
+define i16 @test4() {
+  %r = load i16* getelementptr(i16* bitcast(i32* getelementptr ({{i32,i8},i32}* @test1, i32 0, i32 0, i32 0) to i16*), i32 2)
+  ret i16 %r
+; @test4
+; CHECK: ret i16 186
+}
+
+; Load of double bits.
+define i64 @test6() {
+  %r = load i64* bitcast(double* @test2 to i64*)
+  ret i64 %r
+
+; @test6
+; CHECK: ret i64 4607182418800017408
+}
+
+; Load of double bits.
+define i16 @test7() {
+  %r = load i16* bitcast(double* @test2 to i16*)
+  ret i16 %r
+
+; @test7
+; CHECK: ret i16 0
+}
+
+; Double load.
+define double @test8() {
+  %r = load double* bitcast({{i32,i8},i32}* @test1 to double*)
+  ret double %r
+
+; @test8
+; CHECK: ret double 0xDEADBEBA
+}