[DAGCombine] fold (X >>?,exact C1) << C2 --> X << (C2-C1)

Instcombine also does this but many opportunities only become visible
after GEPs are lowered.

llvm-svn: 240787

1 files changed, 49 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/X86/shift-combine.ll b/llvm/test/CodeGen/X86/shift-combine.ll
index ec62bcdcdba..7fb19a6cad0 100644
--- a/llvm/test/CodeGen/X86/shift-combine.ll
+++ b/llvm/test/CodeGen/X86/shift-combine.ll
@@ -17,3 +17,52 @@ entry:
   ret i32 %tmp5
 }
 
+define i32* @test_exact1(i32 %a, i32 %b, i32* %x)  {
+; CHECK-LABEL: test_exact1:
+; CHECK: sarl %
+
+  %sub = sub i32 %b, %a
+  %shr = ashr exact i32 %sub, 3
+  %gep = getelementptr inbounds i32, i32* %x, i32 %shr
+  ret i32* %gep
+}
+
+define i32* @test_exact2(i32 %a, i32 %b, i32* %x)  {
+; CHECK-LABEL: test_exact2:
+; CHECK: sarl %
+
+  %sub = sub i32 %b, %a
+  %shr = ashr exact i32 %sub, 3
+  %gep = getelementptr inbounds i32, i32* %x, i32 %shr
+  ret i32* %gep
+}
+
+define i32* @test_exact4(i32 %a, i32 %b, i32* %x)  {
+; CHECK-LABEL: test_exact4:
+; CHECK: shrl %
+
+  %sub = sub i32 %b, %a
+  %shr = lshr exact i32 %sub, 3
+  %gep = getelementptr inbounds i32, i32* %x, i32 %shr
+  ret i32* %gep
+}
+
+define i32* @test_exact5(i32 %a, i32 %b, i32* %x)  {
+; CHECK-LABEL: test_exact5:
+; CHECK: shrl %
+
+  %sub = sub i32 %b, %a
+  %shr = lshr exact i32 %sub, 3
+  %gep = getelementptr inbounds i32, i32* %x, i32 %shr
+  ret i32* %gep
+}
+
+define i32* @test_exact6(i32 %a, i32 %b, i32* %x)  {
+; CHECK-LABEL: test_exact6:
+; CHECK-NOT: shrl
+
+  %sub = sub i32 %b, %a
+  %shr = lshr exact i32 %sub, 2
+  %gep = getelementptr inbounds i32, i32* %x, i32 %shr
+  ret i32* %gep
+}