[llvm-commits] [llvm] r44341 - in /llvm/trunk: lib/CodeGen/SelectionDAG/DAGCombiner.cpp test/CodeGen/X86/urem-i8-constant.ll

[Dan Gohman]

Author: djg
Date: Mon Nov 26 17:46:11 2007
New Revision: 44341

URL: http://llvm.org/viewvc/llvm-project?rev=44341&view=rev
Log:
Don't lower srem/urem X%C to X-X/C*C unless the division is actually
optimized. This avoids creating illegal divisions when the combiner is
running after legalize; this fixes PR1815. Also, it produces better
code in the included testcase by avoiding the subtract and multiply
when the division isn't optimized.

Added:
    llvm/trunk/test/CodeGen/X86/urem-i8-constant.ll
Modified:
    llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

Modified: llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
URL: 
http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp?rev=44341&r1=44340&r2=44341&view=diff

==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp Mon Nov 26 17:46:11 2007
@@ -1306,15 +1306,17 @@
       DAG.MaskedValueIsZero(N0, SignBit))
     return DAG.getNode(ISD::UREM, VT, N0, N1);
   
-  // Unconditionally lower X%C -> X-X/C*C.  This allows the X/C logic to hack 
on
-  // the remainder operation.
+  // If X/C can be simplified by the division-by-constant logic, lower
+  // X%C to the equivalent of X-X/C*C.
   if (N1C && !N1C->isNullValue()) {
     SDOperand Div = DAG.getNode(ISD::SDIV, VT, N0, N1);
-    SDOperand Mul = DAG.getNode(ISD::MUL, VT, Div, N1);
-    SDOperand Sub = DAG.getNode(ISD::SUB, VT, N0, Mul);
-    AddToWorkList(Div.Val);
-    AddToWorkList(Mul.Val);
-    return Sub;
+    SDOperand OptimizedDiv = combine(Div.Val);
+    if (OptimizedDiv.Val && OptimizedDiv.Val != Div.Val) {
+      SDOperand Mul = DAG.getNode(ISD::MUL, VT, OptimizedDiv, N1);
+      SDOperand Sub = DAG.getNode(ISD::SUB, VT, N0, Mul);
+      AddToWorkList(Mul.Val);
+      return Sub;
+    }
   }
   
   // undef % X -> 0
@@ -1351,15 +1353,17 @@
     }
   }
   
-  // Unconditionally lower X%C -> X-X/C*C.  This allows the X/C logic to hack 
on
-  // the remainder operation.
+  // If X/C can be simplified by the division-by-constant logic, lower
+  // X%C to the equivalent of X-X/C*C.
   if (N1C && !N1C->isNullValue()) {
     SDOperand Div = DAG.getNode(ISD::UDIV, VT, N0, N1);
-    SDOperand Mul = DAG.getNode(ISD::MUL, VT, Div, N1);
-    SDOperand Sub = DAG.getNode(ISD::SUB, VT, N0, Mul);
-    AddToWorkList(Div.Val);
-    AddToWorkList(Mul.Val);
-    return Sub;
+    SDOperand OptimizedDiv = combine(Div.Val);
+    if (OptimizedDiv.Val && OptimizedDiv.Val != Div.Val) {
+      SDOperand Mul = DAG.getNode(ISD::MUL, VT, OptimizedDiv, N1);
+      SDOperand Sub = DAG.getNode(ISD::SUB, VT, N0, Mul);
+      AddToWorkList(Mul.Val);
+      return Sub;
+    }
   }
   
   // undef % X -> 0

Added: llvm/trunk/test/CodeGen/X86/urem-i8-constant.ll
URL: 
http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/urem-i8-constant.ll?rev=44341&view=auto

==============================================================================
--- llvm/trunk/test/CodeGen/X86/urem-i8-constant.ll (added)
+++ llvm/trunk/test/CodeGen/X86/urem-i8-constant.ll Mon Nov 26 17:46:11 2007
@@ -0,0 +1,6 @@
+; RUN: llvm-as < %s | llc -march=x86 | not grep mul
+
+define i8 @foo(i8 %tmp325) {
+       %t546 = urem i8 %tmp325, 37
+       ret i8 %t546
+}


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