Optimize (x/y)*y into x-(x%y) in general. Div and rem are about the same, and

a subtract is cheaper than a multiply. This generalizes an existing transform.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@59800 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 34 insertions, 0 deletions

diff --git a/test/Transforms/InstCombine/2008-11-20-DivMulRem.ll b/test/Transforms/InstCombine/2008-11-20-DivMulRem.ll
new file mode 100644
index 0000000..8c58a2a
--- /dev/null
+++ b/test/Transforms/InstCombine/2008-11-20-DivMulRem.ll
@@ -0,0 +1,34 @@
+; RUN: llvm-as < %s | opt -instcombine | llvm-dis > %t
+; RUN: grep urem %t | count 3
+; RUN: grep srem %t | count 1
+; RUN: grep sub %t | count 2
+; RUN: grep add %t | count 1
+; PR3103
+
+define i8 @test1(i8 %x, i8 %y) {
+  %A = udiv i8 %x, %y
+  %B = mul i8 %A, %y
+  %C = sub i8 %x, %B
+  ret i8 %C
+}
+
+define i8 @test2(i8 %x, i8 %y) {
+  %A = sdiv i8 %x, %y
+  %B = mul i8 %A, %y
+  %C = sub i8 %x, %B
+  ret i8 %C
+}
+
+define i8 @test3(i8 %x, i8 %y) {
+  %A = udiv i8 %x, %y
+  %B = mul i8 %A, %y
+  %C = sub i8 %B, %x
+  ret i8 %C
+}
+
+define i8 @test4(i8 %x) {
+  %A = udiv i8 %x, 3
+  %B = mul i8 %A, -3
+  %C = sub i8 %x, %B
+  ret i8 %C
+}