gh-95922: compiler's eliminate_empty_basic_blocks ignores the last block of the compilation unit (GH-95924)

iritkatriel · web-flow · commit 41757bfabd26 · 2022-08-12T16:35:09.000+01:00
diff --git a/Misc/NEWS.d/next/Core and Builtins/2022-08-12-13-04-25.gh-issue-95922.YNCtyX.rst b/Misc/NEWS.d/next/Core and Builtins/2022-08-12-13-04-25.gh-issue-95922.YNCtyX.rst
@@ -0,0 +1,2 @@
+Fixed bug where the compiler's ``eliminate_empty_basic_blocks`` function
+ignores the last block of the code unit.
diff --git a/Python/compile.c b/Python/compile.c
@@ -9349,17 +9349,13 @@ eliminate_empty_basic_blocks(basicblock *entryblock) {
     /* Eliminate empty blocks */
     for (basicblock *b = entryblock; b != NULL; b = b->b_next) {
         basicblock *next = b->b_next;
-        if (next) {
-            while (next->b_iused == 0 && next->b_next) {
-                next = next->b_next;
-            }
-            b->b_next = next;
+        while (next && next->b_iused == 0) {
+            next = next->b_next;
         }
+        b->b_next = next;
     }
     for (basicblock *b = entryblock; b != NULL; b = b->b_next) {
-        if (b->b_iused == 0) {
-            continue;
-        }
+        assert(b->b_iused > 0);
         for (int i = 0; i < b->b_iused; i++) {
             struct instr *instr = &b->b_instr[i];
             if (HAS_TARGET(instr->i_opcode)) {
@@ -9368,6 +9364,7 @@ eliminate_empty_basic_blocks(basicblock *entryblock) {
                     target = target->b_next;
                 }
                 instr->i_target = target;
+                assert(instr->i_target && instr->i_target->b_iused > 0);
             }
         }
     }

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	+Fixed bug where the compiler's ``eliminate_empty_basic_blocks`` function
	`2`	`+ignores the last block of the code unit.`
Original file line number	Diff line number	Diff line change
`@@ -9349,17 +9349,13 @@ eliminate_empty_basic_blocks(basicblock *entryblock) {`
`9349`	`9349`	`/* Eliminate empty blocks */`
`9350`	`9350`	`for (basicblock *b = entryblock; b != NULL; b = b->b_next) {`
`9351`	`9351`	`basicblock *next = b->b_next;`
`9352`		`- if (next) {`
`9353`		`- while (next->b_iused == 0 && next->b_next) {`
`9354`		`- next = next->b_next;`
`9355`		`- }`
`9356`		`- b->b_next = next;`
	`9352`	`+ while (next && next->b_iused == 0) {`
	`9353`	`+ next = next->b_next;`
`9357`	`9354`	`}`
	`9355`	`+ b->b_next = next;`
`9358`	`9356`	`}`
`9359`	`9357`	`for (basicblock *b = entryblock; b != NULL; b = b->b_next) {`
`9360`		`- if (b->b_iused == 0) {`
`9361`		`- continue;`
`9362`		`- }`
	`9358`	`+ assert(b->b_iused > 0);`
`9363`	`9359`	`for (int i = 0; i < b->b_iused; i++) {`
`9364`	`9360`	`struct instr *instr = &b->b_instr[i];`
`9365`	`9361`	`if (HAS_TARGET(instr->i_opcode)) {`
`@@ -9368,6 +9364,7 @@ eliminate_empty_basic_blocks(basicblock *entryblock) {`
`9368`	`9364`	`target = target->b_next;`
`9369`	`9365`	`}`
`9370`	`9366`	`instr->i_target = target;`
	`9367`	`+ assert(instr->i_target && instr->i_target->b_iused > 0);`
`9371`	`9368`	`}`
`9372`	`9369`	`}`
`9373`	`9370`	`}`