Merging r233153 and r233584:

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r233153 | probinson | 2015-03-24 17:10:24 -0700 (Tue, 24 Mar 2015) | 7 lines

'optnone' should not disable DAG combiner.

Reverts the code change from r221168 and the relevant test.
It was a mistake to disable the combiner, and based on the ultimate
definition of 'optnone' we shouldn't have considered the test case
as failing in the first place.

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r233584 | probinson | 2015-03-30 12:37:44 -0700 (Mon, 30 Mar 2015) | 9 lines

Verify 'optnone' can run DAG combiner when appropriate.

Adds a test to verify the behavior that r233153 restored: 'optnone'
does not spuriously disable the DAG combiner, and in fact there are
cases where the DAG combiner must run (even at -O0 or 'optnone') in
order for codegen to succeed.

Differential Revision: http://reviews.llvm.org/D8614

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_36@233871 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -1160,13 +1160,6 @@ void DAGCombiner::Run(CombineLevel AtLevel) {
   LegalOperations = Level >= AfterLegalizeVectorOps;
   LegalTypes = Level >= AfterLegalizeTypes;
 
-  // Early exit if this basic block is in an optnone function.
-  AttributeSet FnAttrs =
-    DAG.getMachineFunction().getFunction()->getAttributes();
-  if (FnAttrs.hasAttribute(AttributeSet::FunctionIndex,
-                           Attribute::OptimizeNone))
-    return;
-
   // Add all the dag nodes to the worklist.
   for (SelectionDAG::allnodes_iterator I = DAG.allnodes_begin(),
        E = DAG.allnodes_end(); I != E; ++I)

test/CodeGen/X86/dag-optnone.ll

@@ -0,0 +1,73 @@
+; RUN: llc < %s -mtriple=x86_64-pc-win32 -O0 -mattr=+avx | FileCheck %s
+
+; Background:
+; If fast-isel bails out to normal selection, then the DAG combiner will run,
+; even at -O0. In principle this should not happen (those are optimizations,
+; and we said -O0) but as a practical matter there are some instruction
+; selection patterns that depend on the legalizations and transforms that the
+; DAG combiner does.
+;
+; The 'optnone' attribute implicitly sets -O0 and fast-isel for the function.
+; The DAG combiner was disabled for 'optnone' (but not -O0) by r221168, then
+; re-enabled in r233153 because of problems with instruction selection patterns
+; mentioned above. (Note: because 'optnone' is supposed to match -O0, r221168
+; really should have disabled the combiner for both.)
+;
+; If instruction selection eventually becomes smart enough to run without DAG
+; combiner, then the combiner can be turned off for -O0 (not just 'optnone')
+; and this test can go away. (To be replaced by a different test that verifies
+; the DAG combiner does *not* run at -O0 or for 'optnone' functions.)
+;
+; In the meantime, this test wants to make sure the combiner stays enabled for
+; 'optnone' functions, just as it is for -O0.
+
+
+; The test cases @foo[WithOptnone] prove that the same DAG combine happens
+; with -O0 and with 'optnone' set.  To prove this, we use a Windows triple to
+; cause fast-isel to bail out (because something about the calling convention
+; is not handled in fast-isel).  Then we have a repeated fadd that can be
+; combined into an fmul.  We show that this happens in both the non-optnone
+; function and the optnone function.
+
+define float @foo(float %x) #0 {
+entry:
+  %add = fadd fast float %x, %x
+  %add1 = fadd fast float %add, %x
+  ret float %add1
+}
+
+; CHECK-LABEL: @foo
+; CHECK-NOT:   add
+; CHECK:       mul
+; CHECK-NEXT:  ret
+
+define float @fooWithOptnone(float %x) #1 {
+entry:
+  %add = fadd fast float %x, %x
+  %add1 = fadd fast float %add, %x
+  ret float %add1
+}
+
+; CHECK-LABEL: @fooWithOptnone
+; CHECK-NOT:   add
+; CHECK:       mul
+; CHECK-NEXT:  ret
+
+
+; The test case @bar is derived from an instruction selection failure case
+; that was solved by r233153. It depends on -mattr=+avx.
+; Really all we're trying to prove is that it doesn't crash any more.
+
+@id84 = common global <16 x i32> zeroinitializer, align 64
+
+define void @bar() #1 {
+entry:
+  %id83 = alloca <16 x i8>, align 16
+  %0 = load <16 x i32>* @id84, align 64
+  %conv = trunc <16 x i32> %0 to <16 x i8>
+  store <16 x i8> %conv, <16 x i8>* %id83, align 16
+  ret void
+}
+
+attributes #0 = { "unsafe-fp-math"="true" }
+attributes #1 = { noinline optnone "unsafe-fp-math"="true" }

test/CodeGen/X86/fastmath-optnone.ll

@@ -1,35 +0,0 @@
-; RUN: llc < %s -mcpu=corei7 -march=x86-64 -mattr=+sse2 | FileCheck %s
-; Verify that floating-point operations inside 'optnone' functions
-; are not optimized even if unsafe-fp-math is set.
-
-define float @foo(float %x) #0 {
-entry:
-  %add = fadd fast float %x, %x
-  %add1 = fadd fast float %add, %x
-  ret float %add1
-}
-
-; CHECK-LABEL: @foo
-; CHECK-NOT: add
-; CHECK: mul
-; CHECK-NOT: add
-; CHECK: ret
-
-define float @fooWithOptnone(float %x) #1 {
-entry:
-  %add = fadd fast float %x, %x
-  %add1 = fadd fast float %add, %x
-  ret float %add1
-}
-
-; CHECK-LABEL: @fooWithOptnone
-; CHECK-NOT: mul
-; CHECK: add
-; CHECK-NOT: mul
-; CHECK: add
-; CHECK-NOT: mul
-; CHECK: ret
-
-
-attributes #0 = { "unsafe-fp-math"="true" }
-attributes #1 = { noinline optnone "unsafe-fp-math"="true" }