aboutsummaryrefslogtreecommitdiffstats
path: root/test/CodeGen
diff options
context:
space:
mode:
authorDan Gohman <gohman@apple.com>2008-10-17 01:33:43 +0000
committerDan Gohman <gohman@apple.com>2008-10-17 01:33:43 +0000
commit63f97201dc9dcebbe84d1b73113166c64212b4b8 (patch)
tree718d542a3b0cf7a6c76944afed13d26afbb6a12f /test/CodeGen
parent74feef261a43392bc85280f66c75fbd4e2ccf73d (diff)
downloadexternal_llvm-63f97201dc9dcebbe84d1b73113166c64212b4b8.zip
external_llvm-63f97201dc9dcebbe84d1b73113166c64212b4b8.tar.gz
external_llvm-63f97201dc9dcebbe84d1b73113166c64212b4b8.tar.bz2
Fun x86 encoding tricks: when adding an immediate value of 128,
use a SUB instruction instead of an ADD, because -128 can be encoded in an 8-bit signed immediate field, while +128 can't be. This avoids the need for a 32-bit immediate field in this case. A similar optimization applies to 64-bit adds with 0x80000000, with the 32-bit signed immediate field. To support this, teach tablegen how to handle 64-bit constants. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@57663 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'test/CodeGen')
-rw-r--r--test/CodeGen/X86/add-trick32.ll11
-rw-r--r--test/CodeGen/X86/add-trick64.ll15
2 files changed, 26 insertions, 0 deletions
diff --git a/test/CodeGen/X86/add-trick32.ll b/test/CodeGen/X86/add-trick32.ll
new file mode 100644
index 0000000..42909b4
--- /dev/null
+++ b/test/CodeGen/X86/add-trick32.ll
@@ -0,0 +1,11 @@
+; RUN: llvm-as < %s | llc -march=x86 > %t
+; RUN: not grep add %t
+; RUN: grep subl %t | count 1
+
+; The immediate can be encoded in a smaller way if the
+; instruction is a sub instead of an add.
+
+define i32 @foo(i32 inreg %a) nounwind {
+ %b = add i32 %a, 128
+ ret i32 %b
+}
diff --git a/test/CodeGen/X86/add-trick64.ll b/test/CodeGen/X86/add-trick64.ll
new file mode 100644
index 0000000..5466d9d
--- /dev/null
+++ b/test/CodeGen/X86/add-trick64.ll
@@ -0,0 +1,15 @@
+; RUN: llvm-as < %s | llc -march=x86-64 > %t
+; RUN: not grep add %t
+; RUN: grep subq %t | count 2
+
+; The immediate can be encoded in a smaller way if the
+; instruction is a sub instead of an add.
+
+define i64 @foo(i64 inreg %a) nounwind {
+ %b = add i64 %a, 2147483648
+ ret i64 %b
+}
+define i64 @bar(i64 inreg %a) nounwind {
+ %b = add i64 %a, 128
+ ret i64 %b
+}