fixup! [SPIR-V] Add pre-headers to loops.

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Author: Keenuts

llvm/lib/Target/SPIRV/SPIRVTargetMachine.cpp

@@ -156,6 +156,12 @@ void SPIRVPassConfig::addIRPasses() {
     // Once legalized, we need to structurize the CFG to follow the spec.
     // This is done through the following 8 steps.
     // TODO(#75801): add the remaining steps.
+
+    // 1.  Simplify loop for subsequent transformations. After this steps, loops
+    // have the following properties:
+    //  - loops have a single entry edge (pre-header to loop header).
+    //  - all loop exits are dominated by the loop pre-header.
+    //  - loops have a single back-edge.
     addPass(createLoopSimplifyPass());
   }
 

llvm/test/CodeGen/SPIRV/scfg-add-pre-headers.ll

@@ -4,12 +4,11 @@
 ; CHECK-DAG:    %[[#uint:]] = OpTypeInt 32 0
 ; CHECK-DAG:  %[[#uint_0:]] = OpConstant %[[#uint]] 0
 
-define i32 @main(i32 noundef %0) #1 {
-  %2 = icmp ne i32 %0, 0
-  br i1 %2, label %l1, label %l2
+define void @main() #1 {
+  %1 = icmp ne i32 0, 0
+  br i1 %1, label %l1, label %l2
 
-; CHECK:     %[[#param_0:]] = OpFunctionParameter %[[#uint]]
-; CHECK:        %[[#cond:]] = OpINotEqual %[[#bool]] %[[#param_0]] %[[#uint_0]]
+; CHECK:        %[[#cond:]] = OpINotEqual %[[#bool]] %[[#uint_0]] %[[#uint_0]]
 ; CHECK:                      OpBranchConditional %[[#cond]] %[[#l1_pre:]] %[[#l2_pre:]]
 
 ; CHECK-DAG:   %[[#l2_pre]] = OpLabel
@@ -19,7 +18,7 @@ define i32 @main(i32 noundef %0) #1 {
 ; CHECK-NEXT:                 OpBranch %[[#l1_header:]]
 
 l1:
-  br i1 %2, label %l1_body, label %l1_end
+  br i1 %1, label %l1_body, label %l1_end
 ; CHECK-DAG:    %[[#l1_header]] = OpLabel
 ; CHECK-NEXT:                     OpBranchConditional %[[#cond]] %[[#l1_body:]] %[[#l1_end:]]
 
@@ -39,7 +38,7 @@ l1_end:
 ; CHECK-NEXT:                 OpBranch %[[#end:]]
 
 l2:
-  br i1 %2, label %l2_body, label %l2_end
+  br i1 %1, label %l2_body, label %l2_end
 ; CHECK-DAG:    %[[#l2_header]] = OpLabel
 ; CHECK-NEXT:                     OpBranchConditional %[[#cond]] %[[#l2_body:]] %[[#l2_end:]]
 
@@ -59,7 +58,7 @@ l2_end:
 ; CHECK-NEXT:                 OpBranch %[[#end:]]
 
 end:
-  ret i32 1
+  ret void
 ; CHECK-DAG:       %[[#end]] = OpLabel
 ; CHECK-NEXT:                  OpReturn
 }