[PATCH] D59024: [CGP] Limit distance between overflow math and cmp

[Sam Parker via Phabricator via llvm-commits]

samparker updated this revision to Diff 190065.
samparker added a comment.

Cheers Dave, that's far nicer.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D59024/new/

https://reviews.llvm.org/D59024

Files:
  lib/CodeGen/CodeGenPrepare.cpp
  test/Transforms/CodeGenPrepare/ARM/overflow-intrinsics.ll


Index: test/Transforms/CodeGenPrepare/ARM/overflow-intrinsics.ll
===================================================================
--- /dev/null
+++ test/Transforms/CodeGenPrepare/ARM/overflow-intrinsics.ll
@@ -0,0 +1,56 @@
+; RUN: opt -codegenprepare -S < %s | FileCheck %s
+
+target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
+target triple = "thumbv8m.main-arm-none-eabi"
+
+; CHECK-LABEL: uadd_overflow_too_far_cmp_dom
+; CHECK-NOT: with.overflow.i32
+define i32 @uadd_overflow_too_far_cmp_dom(i32 %arg0) {
+entry:
+  %cmp = icmp ne i32 %arg0, 0
+  br i1 %cmp, label %if.else, label %if.then
+
+if.then:
+  call void @foo()
+  br label %exit
+
+if.else:
+  call void @bar()
+  br label %if.end
+
+if.end:
+  %dec = add nsw i32 %arg0, -1
+  br label %exit
+
+exit:
+  %res = phi i32 [ %arg0, %if.then ], [ %dec, %if.end ]
+  ret i32 %res
+}
+
+; CHECK-LABEL: uadd_overflow_too_far_math_dom
+; CHECK-NOT: with.overflow.i32
+define i32 @uadd_overflow_too_far_math_dom(i32 %arg0, i32 %arg1) {
+entry:
+  %dec = add nsw i32 %arg0, -1
+  %cmp = icmp ugt i32 %arg0, 1
+  br i1 %cmp, label %if.else, label %if.then
+
+if.then:
+  call void @foo()
+  br label %if.end
+
+if.else:
+  call void @bar()
+  br label %if.end
+
+if.end:
+  %cmp.i.i = icmp ne i32 %arg0, 0
+  %tobool = zext i1 %cmp.i.i to i32
+  br label %exit
+
+exit:
+  ret i32 %tobool
+}
+
+declare void @foo()
+declare void @bar()
Index: lib/CodeGen/CodeGenPrepare.cpp
===================================================================
--- lib/CodeGen/CodeGenPrepare.cpp
+++ lib/CodeGen/CodeGenPrepare.cpp
@@ -1183,6 +1183,17 @@
     bool MathDominates = DT.dominates(BO, Cmp);
     if (!MathDominates && !DT.dominates(Cmp, BO))
       return false;
+
+    // Check that the insertion doesn't create a value that is live across more
+    // than two blocks, so to minimise the increase in register pressure.
+    if (BO->getParent() != Cmp->getParent()) {
+      BasicBlock *Dominator = MathDominates ? BO->getParent() : Cmp->getParent();
+      BasicBlock *Dominated = MathDominates ? Cmp->getParent() : BO->getParent();
+      auto Successors = successors(Dominator);
+      if (llvm::find(Successors, Dominated) == Successors.end())
+        return false;
+    }
+
     InsertPt = MathDominates ? cast<Instruction>(BO) : cast<Instruction>(Cmp);
   }
 


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D59024.190065.patch
Type: text/x-patch
Size: 2338 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20190311/362e0977/attachment.bin>