[llvm] r243492 - AArch64: be careful of large immediates when optimising cmps.

[Tim Northover]

Author: tnorthover
Date: Tue Jul 28 17:42:32 2015
New Revision: 243492

URL: http://llvm.org/viewvc/llvm-project?rev=243492&view=rev
Log:
AArch64: be careful of large immediates when optimising cmps.

Modified:
    llvm/trunk/lib/Target/AArch64/AArch64ConditionOptimizer.cpp
    llvm/trunk/test/CodeGen/AArch64/combine-comparisons-by-cse.ll

Modified: llvm/trunk/lib/Target/AArch64/AArch64ConditionOptimizer.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/AArch64/AArch64ConditionOptimizer.cpp?rev=243492&r1=243491&r2=243492&view=diff
==============================================================================
--- llvm/trunk/lib/Target/AArch64/AArch64ConditionOptimizer.cpp (original)
+++ llvm/trunk/lib/Target/AArch64/AArch64ConditionOptimizer.cpp Tue Jul 28 17:42:32 2015
@@ -154,11 +154,18 @@ MachineInstr *AArch64ConditionOptimizer:
     // cmn is an alias for adds with a dead destination register.
     case AArch64::ADDSWri:
     case AArch64::ADDSXri:
-      if (MRI->use_empty(I->getOperand(0).getReg()))
-        return I;
-
-      DEBUG(dbgs() << "Destination of cmp is not dead, " << *I << '\n');
-      return nullptr;
+      if (!I->getOperand(2).isImm()) {
+        DEBUG(dbgs() << "Immediate of cmp is symbolic, " << *I << '\n');
+        return nullptr;
+      } else if (I->getOperand(2).getImm() << I->getOperand(3).getImm() >=
+                 0xfff) {
+        DEBUG(dbgs() << "Immediate of cmp may be out of range, " << *I << '\n');
+        return nullptr;
+      } else if (!MRI->use_empty(I->getOperand(0).getReg())) {
+        DEBUG(dbgs() << "Destination of cmp is not dead, " << *I << '\n');
+        return nullptr;
+      }
+      return I;
 
     // Prevent false positive case like:
     // cmp      w19, #0

Modified: llvm/trunk/test/CodeGen/AArch64/combine-comparisons-by-cse.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/AArch64/combine-comparisons-by-cse.ll?rev=243492&r1=243491&r2=243492&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/AArch64/combine-comparisons-by-cse.ll (original)
+++ llvm/trunk/test/CodeGen/AArch64/combine-comparisons-by-cse.ll Tue Jul 28 17:42:32 2015
@@ -403,6 +403,32 @@ return:
   ret i32 %retval.0
 }
 
+define void @cmp_shifted(i32 %in, i32 %lhs, i32 %rhs) {
+; CHECK-LABEL: cmp_shifted:
+; CHECK: cmp w0, #1
+; [...]
+; CHECK: cmp w0, #2, lsl #12
+
+  %tst_low = icmp sgt i32 %in, 0
+  br i1 %tst_low, label %true, label %false
+
+true:
+  call i32 @zoo(i32 128)
+  ret void
+
+false:
+  %tst = icmp sgt i32 %in, 8191
+  br i1 %tst, label %truer, label %falser
+
+truer:
+  call i32 @zoo(i32 42)
+  ret void
+
+falser:
+  call i32 @zoo(i32 1)
+  ret void
+}
+
 declare i32 @zoo(i32)
 
 declare double @yoo(i32)